RCDB conditions python

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Introduction

Run conditions is the way to store information related to a run (which is identified by run_number everywhere). From a simplistic point of view, run conditions are presented in RCDB as name-value pairs attached to a run number. For example, event_count = 1663 for run 100.


More versatile options of conditions include:

  • A condition can also hold a time information of occurrence name - value (+time)
  • Several values could be attached by the same name to the same run. So it looks like name - [(value1, time1), (value2, time2), ... ]
  • As opposite, API can ensure that there in strictly one value per run
  • Different types of values are supported


This tutorial covers RCDB conditions python API, which provides complete tooling for conditions management. The API is developed using SQLAlchemy ORM, which unifies workflow for MySQL and SQLite databases (and many more, actually). RCDB API hides many complexities of SQLAlchemy and provides simple and very straightforward functions to manage conditions. But users can use all power of SQLAlchemy for querying and filtering results if they wish.


Lets see how python code would look for the example above. Read event_count for run 100: 

# Open SQLite database connection
db = rcdb.RCDBProvider("sqlite:///path.to.file.db")
 
# Read value for run 100
event_count = db.get_condition(100, "event_count").value


Write event_count=1663 for run 100: 

# Once in a lifetime, create a condition type, that defines event_count
ct = db.create_condition_type("event_count", ConditionType.INT_FIELD, False)
 
# Write condition value to run 100
db.add_condition(100, "event_count", 1663)


What RCDB conditions is not designed for? - If data is bulky and changes rarely (value is the same for many runs), it is better not to save it using conditions. That is because each value is independently saved and attached to a run. RCDB provides file saving mechanism for such kind of bulk data. Or maybe CCDB fits better in this case.


Installation

1. Get rcdb.

RCDB svn is:

https://halldsvn.jlab.org/repos/trunk/online/daq/rcdb/rcdb


2. Set environment.

There are *environment.bash* or *environment.csh* scripts, which automatically set environment variables for the of rcdb 

source environment.bash

The script:

  • sets $RCDB_HOME - to RCDB root directory,
  • appends $PYTHONPATH with $RCDB_HOME/python
  • appends $PATH with rcdb bin folder


3.Choose database

The main database is considered to be MySQL in counting house. The connection string is: 

mysql://rcdb:<whell_known_pwd>@gluondb/rcdb

SQLite database snapshot is also available at: 

/u/group/halld/Software/rcdb


To experiment with RCDB and examples below, there is create_empty_sqlite.py script in $RCDB_HOME/python folder. The script creates empty sqlite database. The usage is: 

python $RCDB_HOME/python/create_empty_sqlite.py path_to_database.db


ALL YOU HAVE TO KNOW example

At least to start with RCDB conditions, to put values and to get them back: 

from datetime import datetime
from rcdb.provider import RCDBProvider
from rcdb.model import ConditionType
 
# 1. Create RCDBProvider object that connects to DB and provide most of the functions
db = RCDBProvider("sqlite:///example.db")
 
# 2. Create condition type. It is done only once
db.create_condition_type("my_val", ConditionType.INT_FIELD, is_many_per_run=False, description="This is my value")
 
# 3. Add data to database
db.add_condition(1, "my_val", 1000)
 
# Replace previous value
db.add_condition(1, "my_val", 2000, replace=True)
 
# 4. Get condition from database
condition = db.get_condition(1, "my_val")
 
print condition
print "value =", condition.value
print "name  =", condition.name

The script result: 

<Condition id='1', run_number='1', value=2000>
value = 2000
name  = my_val


A little more advanced actions: 

# 5. Get all existing conditions names and their descriptions
for ct in db.get_condition_types():
    print ct.name, ':', ct.description


The script result: 

my_val : This is my value



# 6. Get all values for the run 1
run = db.get_run(1)
print "Conditions for run {}".format(run.number)
for condition in run.conditions:
    print condition.name, '=', condition.value


The script result: 

my_val = 2000


The example also available as: 

$RCDB_HOME/python/example_conditions_basic.py


It is assumed that 'example.db' is SQLite database, created by *create_empty_sqlite.py* script. To run it: 

python $RCDB_HOME/python/create_empty_sqlite.py example.db
python $RCDB_HOME/python/example_conditions_basic.py

(!) note that to run the script again you probably have to delete the database rm example.db

The next sections will cover this example and give thorough explanation on what is here.


Connection

db = RCDBProvider("sqlite:///example.db")

RCDBProvider is an object that holds database session and provides connect/disconnect functions. It uses connection strings to pass database parameters to the class. It also also carry functions to manage run condition and other RCDB data.


The functions usually return database model objects (described right in the next section). Additional manipulations over this objects could be done with SQLAlchemy (described later).


For now we consider to use MySQL and SQLite databases. The connection strings for them are:

MySQL 

mysql://user_name:password@host:port/database


SQLite 

sqlite:///path_to_file

(!) Note that because SQLite doesn't have user_name and password, it starts with three slashes ///. And thus there are four slashes //// in absolute path to file. 

sqlite:////home/user/example.db


More about connections could be found in [SQLAlchemy documentation]


In the example above class constructor is used to connect to database. But there are more connection functions: 

# Create provider without connecting
db = RCDBProvider()
 
# Connect to database
db.connect("sqlite:///example.db")
 
# check connection and get connection string from provider
if db.is_connected:
    print "connected to:", db.connection_string
 
#disconnect from DB
db.disconnect()

(!) Note that connect function doesn't really connect to database. It just creates so called engine and session objects using the connection string. Thus, connect function raises exceptions if the connection string has wrong format or there is no required libraries in the system. But if there is no physical connection to MySQL or there is no such SQLite file, the function doesn't raise eny errors. The errors are raised on first data retrieval in such case.


Data model

Database structure

At the database level conditions part presented as 3 tables: 


RUNS              CONDITIONS         CONDITION_TYPES
 number    <--     run_num            name
                   type_id     -->    field_type
                   *_value            is_many_per_run
                   time


So when we talk about name-value pair for the run, this actually means that:

  • Run number and other run information (like times of start and end) is stored in the runs table.
  • Names and type of value are stored in the condition_types table.
  • And, finally, values are stored in the conditions table, each record of it is referenced to a run and to a condition_type.


Python class structure

Python API data model classes resembles this structure. There are 3 python classes that you work with:

  • Run - represents run
  • Condition - stores data for the run
  • ConditionType - stores condition name, field type and other


All classes have properties to reference each other. The main properties for conditions management are: 

class Run(ModelBase):
    number                  # int - The run number
    start_time              # datetime - Run start time
    end_time                # datetime - Run end time
    conditions              # list[Condition] - Conditions associated with the run
 
 
class ConditionType(ModelBase):
    name               # str(max 255) - A name of condition
    value_type         # str(max 255) - Type name. One of XXX_FIELD (see  below)
    is_many_per_run    # bool- True if the value is allowed many times per run
    values             # query[Condition] - query to look condition values for runs
 
    # Constants, used for declaration of value_type
    STRING_FIELD = "string"
    INT_FIELD = "int"
    BOOL_FIELD = "bool"
    FLOAT_FIELD = "float"
    JSON_FIELD = "json"
    BLOB_FIELD = "blob"
    TIME_FIELD = "time"
 
 
class Condition(ModelBase):
    time           # datetime - time related to condition (when it occurred in example)
    run_number     # int - the run number
 
    @property
    value          # int, float, bool or string - depending on type. The condition value
 
    text_value     # holds data if type STRING_FIELD,JSON_FIELD or BLOB_FIELD
    int_value      # holds data if type INT_FIELD
    float_value    # holds data if type FLOAT_FIELD
    bool_value     # holds data if type BOOL_FIELD
 
    run            # Run - Run object associated with the run_number
    type           # ConditionType - link to associated condition type
    name           # str - link to type.name. See ConditionType.name
    value_type     # str - link to type.value_type. See ConditionType.value_type


How data is stored in the DB

As you may noticed from comments above, in reality data is stored in one of the fields:

Storage field Value type
text_value STRING_FIELD, JSON_FIELD or BLOB_FIELD
int_value INT_FIELD
float_value FLOAT_FIELD
bool_value BOOL_FIELD

When you call Condition.value property, Condition class checks for type.value_type and returns an appropriate xxx_value.


Why is it so? - because we would like to have queries like: "give me runs where event_count > 100 000"

i.e., if we know that event_count is int, we would like database to operate it as int.

At the same time we would like to store strings and more general data with blobs. To have it, RCDB uses so called "hybrid approach to object-attribute-value model". If value is int, float, bool or time, it is stored in appropriate field, which allows to use its type when querying. Finally it is possible search over ints, floats and time and, at the same time, to store more complex objects as JSON or blobs... to figure out them lately


Creating condition types

To save data in run conditions, a "condition type" should be created first. It is done once in a database lifetime. Lets look create_condition_type from the example above (we add parameter names here): 

db.create_condition_type(name="my_val",
                         value_type=ConditionType.INT_FIELD,
                         is_many_per_run=False,
                         description="This is my value")


name - The first parameter is condition name. When we say "event_count for run 100", "event_count" is that name. Names are case sensitive. The API doesn't validate names for any name convension and there is no built in checking for spaces. But spaces would definitely make problems so are not recommended.

It is possible to have names like: 

category/sub/name
category-sub-name
category-sub_name

Names are just strings. RCDB doesn't provide special treatment of slashes '/' or directories.


value_type - The second parameter defines type of the value. It can be one of:

  • ConditionType.STRING_FIELD
  • ConditionType.INT_FIELD
  • ConditionType.BOOL_FIELD
  • ConditionType.FLOAT_FIELD
  • ConditionType.TIME_FIELD
  • ConditionType.JSON_FIELD
  • ConditionType.BLOB_FIELD

More examples of how to use types are presented in the next section


is_many_per_run - Allows to store many values with different time for the same run

  • False - API works as name - value(time), i.e. it checks that there is only one value per run
  • True - API allows name - [(value1, time1), (value2, time2), ...] scheme.


Explanation - There are two different behaviours that are assumed for run conditions: Sometimes it is intended to have strictly one name-value for a run. "total_events" or "target_material" are the examples. If is_many_per_ru=False, then API checks that there is only one value per run. But the sometimes it is desirable to track value change during a run. Hall "temperature" or "current" are those examples. If is_many_per_run=True, then API allows to set several values for different times under the same name for the same run

More examples on it is given in #Replacing previous values


description - 255 chars max human readable description, that other users can see. It is optional but it is very good practice to fill it.

Adding data to database

Basic types: int, float, bool, string

To store basic types one of the fields should be used:

  • ConditionType.STRING_FIELD
  • ConditionType.INT_FIELD
  • ConditionType.BOOL_FIELD
  • ConditionType.FLOAT_FIELD


Lets example it: 

# Create RCDBProvider provider object and connect it to DB
db = RCDBProvider("sqlite:///example.db")
 
# Crete condition types
db.create_condition_type("int_val", ConditionType.INT_FIELD, False)
db.create_condition_type("float_val", ConditionType.FLOAT_FIELD, False)
db.create_condition_type("bool_val", ConditionType.BOOL_FIELD, False)
db.create_condition_type("string_val", ConditionType.STRING_FIELD, False)
 
# Add values to run 1
db.add_condition(1, "int_val", 1000)
db.add_condition(1, "float_val", 2.5)
db.add_condition(1, "bool_val", True)
db.add_condition(1, "string_val", "test test")
 
# Read values for run 1 and use them
 
condition = db.get_condition(1, "int_val")
print condition.value
 
condition = db.get_condition(1, "float_val")
print condition.value
 
condition = db.get_condition(1, "bool_val")
print condition.value
 
condition = db.get_condition(1, "string_val")
print condition.value

The output: 

1000
2.5
True
test test


Time information

A time information can be attached to any condition value. Standard python datetime is used for that: (Lets see the first example): 

# Create condition type
db.create_condition_type("my_val", ConditionType.INT_FIELD, False)
 
# Add value and time information
db.add_condition(1, "my_val", 2000, datetime(2015, 10, 10, 15, 28, 12, 111111))
 
# Get condition from database
condition = db.get_condition(1, "my_val")
 
print condition
print "value =", condition.value
print "name  =", condition.name
print "time  =", condition.time

The output is: 

<Condition id='1', run_number='1', value=2000>
value = 2000
name  = my_val
time  = 2015-10-10 15:28:12.111111


If time is the only relevant information for a condition, then ConditionType.TIME_FIELD type can be used to create the condition type. In this case Condition.value field will have time information and time can be passed as value parameter of add_condition function: 

db.create_condition_type("lunch_bell_rang", ConditionType.TIME_FIELD, False)
 
# add value to run 1
time = datetime(2015, 9, 1, 14, 21, 01)
db.add_condition(1, "lunch_bell_rang", time)
 
# get from DB
val = self.db.get_condition(1, "lunch_bell_rang")
print val.value
print val.time

The output is: 

2015-09-01 14:21:01
2015-09-01 14:21:01

Note that val.value and val.time are the same in this example.


Multiple values per run

To add many values of the same type, is_many_per_run parameter of create_condition_type function should be set to True. Then you are able to add many condition values per one run, but specifying time for each of them.


(!) if is_many_per_run=True, then get_condition returns a list of Condition objects. <inc>Even</inc> 

if there is only one object selected.

Example 

# Many condition values allowed for the run (is_many_per_run=True)
#    1. If run has this condition, with the same value and actual_time the func. DOES NOTHING
#    2. If run has this conditions but at different time, it adds this condition to DB
 
db.create_condition_type("multi", ConditionType.INT_FIELD, True)
 
time1 = datetime(2015,9,1,14,21,01, 222)
time2 = datetime(2015,9,1,14,21,01, 333)
 
# First addition to DB. Time is None
db.add_condition(1, "multi", 2222)
 
# Ok. Value for time1 is added to DB
db.add_condition(1, "multi", 3333, time1)
db.add_condition(1, "multi", 4444, time2)
 
results = db.get_condition(1, "multi")
 
# We should get 3 values as:
# 0: value=2222; time=None
# 1: value=3333; time=time1
# 2: value=4444; time=time2
# lets check it
print results
values = [result.value for result in results]
times = [result.time for result in results]
print values
print times

The output: 

[<Condition id='1', run_number='1', value=2222>, <Condition id='2', run_number='1', value=3333>, <Condition id='3', run_number='1', value=4444>]
[2222, 3333, 4444]
[None, datetime(2015, 9, 1, 14, 21, 1, 222), datetime(2015, 9, 1, 14, 21, 1, 333)]


Arrays and dictionaries

Multiple values per run are NOT intended to store arrays of data.


Best way to store arrays and dictionaries is serializing them to JSON. Use ConditionType.JSON_FIELD for that. RCDB conditions API doesn't provide mechanisms of converting objects to JSON and from JSON. For arrays it is done easily by json module.


The example from [python 2.7 documentation]: 

>>> import json
>>> json.dumps(['foo', {'bar': ('baz', None, 1.0, 2)}])
 '["foo", {"bar": ["baz", null, 1.0, 2]}]'
 
>>> json.loads('["foo", {"bar":["baz", null, 1.0, 2]}]')
 [u'foo', {u'bar': [u'baz', None, 1.0, 2]}]

So, serialization is on your side. It is done to have a better control over serialization. This means that if condition type is JSON_FIELD, add_condition function awaits string and after you get condition back, Condition.value contains string.


Example: 

import json
from rcdb.provider import RCDBProvider
from rcdb.model import ConditionType
 
# Create RCDBProvider provider object and connect it to DB
db = RCDBProvider("sqlite:///example.db")
 
# Create condition type
db.create_condition_type("list_data", ConditionType.JSON_FIELD, False)
db.create_condition_type("dict_data", ConditionType.JSON_FIELD, False)
 
list_to_store = [1, 2, 3]
dict_to_store = {"x": 1, "y": 2, "z": 3}
 
# Dump values to JSON and save it to DB to run 1
db.add_condition(1, "list_data", json.dumps(list_to_store))
db.add_condition(1, "dict_data", json.dumps(dict_to_store))
 
# Get condition from database
restored_list = json.loads(db.get_condition(1, "list_data").value)
restored_dict = json.loads(db.get_condition(1, "dict_data").value)
 
print restored_list
print restored_dict
 
print restored_dict["x"]
print restored_dict["y"]
print restored_dict["z"]

The output is: 

[1, 2, 3]
{u'y': 2, u'x': 1, u'z': 3}
1
2
3


The example is located at 

$RCDB_HOME/python/example_conditions_store_array.py

and can be run as: 

python $RCDB_HOME/python/create_empty_sqlite.py example.db
python $RCDB_HOME/python/example_conditions_store_array.py

As one can mention unicode string is returned as unicode after json deserialization (look at u"x" instead of just "x"). It is not a problem if you just work with this array, because python acts seamlessly with unicode strings. As you can see in example, we use usual string "x" in restored_dict["x"] and it just works.

If it is a problem, there is a [stackoverlow question on that]

Using pyYAML to deserialize to strings looks easy.


Custom python objects

To save custom python objects to database, jsonpickle package could be used. It is an open source project available via pip install. It is not shipped with RCDB at the moment. 

from rcdb.provider import RCDBProvider
from rcdb.model import ConditionType
import jsonpickle
 
 
class Cat(object):
    def __init__(self, name):
        self.name = name
        self.mice_eaten = 1230
 
 
# Create RCDBProvider provider object and connect it to DB
db = RCDBProvider("sqlite:///example.db")
 
# Create condition type
db.create_condition_type("cat", ConditionType.JSON_FIELD, False)
 
 
# Create a cat and store in in the DB for run 1
cat = Cat('Alice')
db.add_condition(1, "cat", jsonpickle.encode(cat))
 
# Get condition from database for run 1
condition = db.get_condition(1, "cat")
loaded_cat = jsonpickle.decode(condition.value)
 
print "How cat is stored in DB:"
print condition.value
print "Deserialized cat:"
print "name:", loaded_cat.name
print "mice_eaten:", loaded_cat.mice_eaten

The result: 

How cat is stored in DB:
{"py/object": "__main__.Cat", "name": "Alice", "mice_eaten": 1230}
Deserialized cat:
name: Alice
mice_eaten: 1230


[jsonpickle Documentation]

jsonpickle installation:

system level: 

pip install jsonpickle

user level: 

pip install --user jsonpickle


STRING_FIELD vs. JSON_FIELD vs. BLOB_FIELD

What if data doesn't fit into the string or JSON? There is ConditionType.BLOB_FIELD type.

Concise instruction is much like JSON:

  • Set condition type as BLOB_FIELD
  • You serialize object whatever you like
  • Save it to DB as string
  • Load from DB
  • Deserialize whatever you like


But what is the difference between STRING_FIELD, JSON_FIELD and BLOB_FIELD?


There is no difference in terms of storing the data. A Condition class, same as a database table, has text_value field where text/string data is stored. The ONLY difference is how this fields are treated and presented in GUI.

  • STRING_FIELD - is considered to be a human readable string.
  • JSON_FIELD - is considered to be JSON, which is colored and formatted accordingly
  • BLOB_FIELD - is considered to be neither very readable string nor JSON. But it is still should converted to some string. And I hope it will never be used.



Replacing previous values

What if the condition value for this run with this name already exists in the DB?

In general, to replace value replace=True parameter should be set in add_condition.

For single value per run: 1. If run has this condition, with the same value and time, exception is not raised and function does nothing. 2. If value OR actual_time is different than in DB, function checks 'replace' flag and behave accordingly to it

Example: 

db.add_condition(1, "event_count", 1000)                  # First addition to DB
db.add_condition(1, "event_count", 1000)                  # Ok. Do nothing, such value already exists
db.add_condition(1, "event_count", 2222)                  # Error. OverrideConditionValueError
db.add_condition(1, "event_count", 2222, replace=True)    # Ok. Replacing existing value
print(db.get_condition(1, "event_count"))
#   value: 2222
#   time:  None
 
time1 = datetime(2015,9,1,14,21,01, 222)
time2 = datetime(2015,9,1,14,21,01, 333)
db.add_condition(1, "timed", 1, time1)        # First addition to DB
db.add_condition(1, "timed", 1, time1)        # Ok. Do nothing
db.add_condition(1, "timed", 1, time2)        # Error. Time is different
db.add_condition(1, "timed", 5, time1)        # Error. Value is different
db.add_condition(1, "timed", 5, time2, True)  # Ok. Value replaced
 
print(db.get_condition(1, "timed"))
#   value: 5
#   time:  time2


If many condition values allowed for the run (is_many_per_run=True)

  1. If run has this condition, with the same value and same time the func. DOES NOTHING
  2. If run has this conditions but at different time, it adds this condition to DB
  3. If run has this condition at this time


Example: 

time1 = datetime(2015,9,1,14,21,01, 222)
time2 = datetime(2015,9,1,14,21,01, 333)
db.add_condition(1, "event_count", 1000)                  # First addition to DB. Time is None
db.add_condition(1, "event_count", 1000)                  # Ok. Do nothing, such value already exists
db.add_condition(1, "event_count", 2222)                  # Error. Another value for time None
db.add_condition(1, "event_count", 2222, replace=True)    # Ok. Replacing existing value for time None
db.add_condition(1, "event_count", 3333, time1)           # Ok. Value for time1 is added to DB
db.add_condition(1, "event_count", 4444, time1)           # Error. Value differs for time1
db.add_condition(1, "event_count", 4444, time2)           # Ok. Add 444 for time2 to DB
 
print(db.get_condition(1, "event_count"))
 # [0: value=2222; time=None
 #  1: value=3333; time=time1
 #  2: value=4444; time=time2]



SQLAlchemy

SQLAlchemy makes link between python classes and related database tables. It loads data from DB to classes and when objects are changed, can commit changes back to DB. Also SQLAlchemy glues the classes and makes it possible to navigate between objects.

Lets see a code example: 

# open database
db = rcdb.RCDBProvider("sqlite:///example.db")
 
# get Run object for the run number 1
run = db.get_run(1)
 
# now we have access to all conditions for that run as
run.conditions
 
# get all condition names or all condition values
 
names = [condition.name for condition in run.conditions]
values = [condition.values for condition in run.conditions]

SQLAlchemy makes queries to database if needed. So when you do run = self.db.get_run(1), Run.conditions collection is not yet loaded from DB. It actually isn't loaded even when we do like x=run.conditions. But first time when a real value is needed, database is queried for all conditions for that run.


Editing or deleting objects

Even if overriding of existing values are possible for RCDB, deleting data or editing existing condition types considered to be avoided. But sometimes it is needed. Especially at the development/debugging phase.


To edit or delete things SQLAlchemy session object can be used.


Editing

Edit condition type 

# get condition type
condition_type = db.get_condition_type("my_var")
 
# Change what you need
condition_type.value_type = ConditionType.JSON_FIELD
 
# Calling session commit will save changes to database
db.session.commit()


Rename condition 

# get condition type
condition_type = db.get_condition_type("my_var")
 
# Change what you need
condition_type.name = "new_var"
 
# Calling session commit will save changes to database
db.session.commit()

The magic is that all data for all runs are now accessible by new_var


Deleting

Deleting objects is done with session.delete function: 

# Edit condition type
condition_type = db.get_condition_type("my_var")
 
# mark the object for deletion
db.session.delete(condition_type)
 
# Calling session commit will save changes to database
db.session.commit()

More about session and SQLAlchemy objects manipulation with it can be found in [SQLAlchemy documentation]



Database querying

Working with runs

If you ever want to get Run object by run_number here is how: 

run = db.get_run(run_number)
print run.number
print run.start_time
print run.end_time
print run.conditions... # but it is written further

How to query runs is shown far below


Get runs by number (or intruduction to SQLAlchemy queries)

Lets select all runs with run_number < 100 using SQLAlchemy 

# open database
db = rcdb.RCDBProvider("sqlite:///example.db")
 
# create query
query = db.session.query(Run).filter(Run.number < 100)
 
# get count of selected runs
print query.count()
 
# get first run from selected
print query.first()
 
# get all run that matches the creteria
print query.all()

What happened?

db.session - gets SQLAlchemy session object

.query(Run) - here we say, that we want Run objects to be returned. At the same time we say what table we want to query

.filter(Run.number < 100) - filtering clause

When we've got query ready, we can actually get objects by query.first() or query.all() (there are actually more) or just count number of runs by query.count()

We can use Run.conditions to get conditions for each run. Lets see more advanced example 

# open database
db = rcdb.RCDBProvider("sqlite:///example.db")
 
# create query
query = db.session.query(Run)
    .filter(Run.number.between(50,55)
    .order_by(desc(Run.number))
 
# get all such runs
runs = query.all()
for run in runs:
    event_count, = (condition.value for condition in run.conditions if condition.name=='event_count')

It works and looks easy. But there is one drawback, each selected run will call one SELECT QUERY to DB to get its conditions. If might be OK for many cases.


Raw SQLAlchemy queries

What if we want to select runs by conditions value?


First, lets say, that if RCDBProvider gives access to SQLAlchemy session, then it is possible to make use of full power of SQLAlchemy queries.


Lets say, we want to get all runs with event_count > 100 000 

# open database
db = rcdb.RCDBProvider("sqlite:///example.db")
 
# create query
query = db.session.query(Run).join(Run.conditions).join(Condition.type)\
        .filter(ConditionType.name == "event_count")\
        .filter(Condition.int_value > 100 000)\
        .order_by(Run.number)
 
 
# get count of selected runs
print query.count()
 
# get first run from selected
print query.first()
 
# get all run that matches the creteria
print query.all()


What happened here.

By first line: 

query = db.session.query(Run).join(Run.conditions).join(Condition.type)\

we say, that we would like to select Run objects (.query(Run)), and also that we will use conditions and condition types (.join(Run.conditions).join(Condition.type)).


Then we filter results (.filter(...)) and ask results to by ordered by Run.number (.order_by(Run.number))


All these functions (join, filter, order_by, ...) returns Query object, that allows to stack them as many as needed.


Finally, to get the results, one of query.count(), query.first(), query.one() or query.all() is called.


But probably you already feel drawbacks of this approach:

  • First, you see that you have to use int_value to filter conditions. That by many means worse than using Condition.value property, that handles type automatically.
  • Another drawback is that when you add more logic, the query becomes bulky.


Lets imagine next example. We look for run in range 1000 to 2000 with event_count > 10000, some data_value in range 1.2 and 2.4 

query = db.session.query(Run).join(Run.conditions).join(Condition.type)\
    .filter(Run.number.between(1000, 2000)\
    .filter(((ConditionType.name == "event_count") & (Condition.int_value > 10000)) |
            ((ConditionType.name == "data_value") & (Condition.float_value.between(1.2, 2.4))))\
    .order_by(Run.number)
 
print query.all()


Note that instead of common && and ||, & and | is used. SQLAlchemy overloads this operators to use for comparison.

Note also, that such expressions should be in parentheses. It is possible to use or_ and and_ functions instead, but it doesn't improve the readability.


Querying using RCDB helpers

RCDB ConditionType provide helpful properties to make querying easier. 

# get condition type
t = db.get_condition_type("event_count")
 
# select runs where event_count > 1000
query = t.run_query.filter(t.value_field > 1000)
 
print query.all()


What happened?

  • run_query - returns query bootstrap that selects Run objects for given type. So it hides this thing from the raw query above:
....query(Run).join(Run.conditions).join(Condition.type) ... .filter(((ConditionType.name == "event_count")


  • value_field - returns the right Condition.xxx_value for a given type. When you put t.value_field > 1000 here, ConditionType t looked at his value_type and selected the right Condition.int_value to compare


But there is a limitation. Each condition type should has its own query. But queries can be combined by union or intersect methods later.


Lets look at the example, where we fill DB with dummy data and then query for runs using the helper properties. The same example can be found in $RCDB_HOME/python/example_conditions_query.py 

# create in memory SQLite database
db = rcdb.RCDBProvider("sqlite://")
rcdb.model.Base.metadata.create_all(db.engine)
 
# create conditions types
event_count_type = db.create_condition_type("event_count", ConditionType.INT_FIELD, False)
data_value_type = db.create_condition_type("data_value", ConditionType.FLOAT_FIELD, False)
 
# create runs and fill values
for i in range(0, 100):
    db.create_run(i)
    db.add_condition(i, event_count_type, i + 950)      #event_count in range 950 - 1049
    db.add_condition(i, data_value_type, (i/100.0) + 1) #data_value in 1 - 2
 
 
""" Demonstrates ConditionType query helpers"""
event_count_type = db.get_condition_type("event_count")
data_value_type = db.get_condition_type("data_value")
 
# select runs where event_count > 1000
query = event_count_type.run_query.filter(event_count_type.value_field > 1000).filter(Run.number <=53)
print query.all()
 
# select runs where 1.52 < data_value < 1.7
query2 = data_value_type.run_query
    .filter(data_value_type.value_field.between(1.52, 1.7))\
    .filter(Run.number < 55)
print query2.all()
 
# combine results of this two queries
print "Results intersect:"
print query.intersect(query2).all()
print "Results union:"
print query.union(query2).all()

The output is: 

[<Run number='51'>, <Run number='52'>, <Run number='53'>]
[<Run number='52'>, <Run number='53'>, <Run number='54'>]

Results intersect:
[<Run number='52'>, <Run number='53'>]

Results union:
[<Run number='51'>, <Run number='52'>, <Run number='53'>, <Run number='54'>]


More on SQLAlchemy queries in SQLAlchemy querying tutorial SQLAlchemy Query API


The example is available as 

python $RCDB_HOME/python/example_conditions_query.py

(It creates inmemory database so there is no need in creaty_empty_sqlite.py)



Logging

RCDB have a logging system which stores some information about what is going on in the same database in *'log_records'* table.


Set RCDB_USER environment variable to have your name in logs (or set it manually in API as shown below)


  • Creating condition types goes to log automatically
  • All condition values manipulations are not logged

It is done in assumption, that the database has many runs and each run has many condition values, so if each condition value creation will have text log message, the database will be bloated with log records.


From the other point of view, when you do a series of operations with conditions it may be a good idea to left a log message that could be seen by other users.


Custom data modification by SQLAlchemy, like creating or deleting objects manually with session.commit() is not logged too, so log notification is left to user here too.


How to left a log record: 

# set RCDB_USER environment variable to give RCDB you user name
# another option is to give it in constructor
db = RCDBProvider("sqlite:///example.db", user_name="john")
 
# and one more option of setting user name
db.user_name = "john"
 
# simplest log version
db.add_log_record(None, "Hello everybody! You'll see this message in logs on RCDB site", 0)

First None means there is no specific database object ID for this message. The last '0' means there is no specific run number for this message



Support

Dmitry Romanov <romanov@jlab.org>

DescriptionDescription of how to manage RCDB run conditions using python API

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