sqlalchemy-capture-sql

A small library that enables capturing SQLAlchemy SQL statements / queries.

Django has django.db.connection.queries connection property that enables user to display executed raw SQL queries (DEBUG mode only). Sometimes in debugging or unit testing this can serve the purpose to check and control nr. and type of sql statements executed for monitored case.

This library provides simple class that enables similar behaviour, but for SQLAlchemy. Each SQL statement is captured along with passed parameters.

How it works

Internally it uses event.listens_for(engine, 'before_cursor_execute' event handler, e.g.:

@event.listens_for(engine, 'before_cursor_execute')
def capture_sa_statement_listener(...)

It simply collects all sql statements sent to event listeer by SQLAlchemy (sent just before execution) and statements are collected in CaptureSqlStatements instance until .finish() method is called (or with ctx is exited).

Additionally it provides time measurement (see REMARKS), stats and formatting functions, see Examples.

REMARKS

Some remarks:

• There is some "heuristic" duration measurement, i.e. class measures time between 2 captures, it is not actual DB execution time.

• Capturing type of command and table name is very simple and one should not rely on it.

Tested and developed on Python 3.7+SQLAlchemy 1.3, but I assume it should work on later and probably some previous versions.

Installation

As usual:

pip install sqlalchemy-capture-sql

Example usage

Some very simple examples using factory-boy classes, more to come.

with with python statement:

with CaptureSqlStatements(engine_cloud) as capture_stmts:
    # put here any calls that issue sqlalchemy commands that produce some
    # sql statements execution.
    cpm = FactoryModel.create()
    # no .finish() needed
capture_stmts.pp(short=True)

standard style:

capture_stmts = CaptureSqlStatements(engine_cloud)
# put here any calls that issue sqlalchemy commands that produce some
# sql statements execution.
cpm = FactoryModel.create()
capture_stmts.finish()
capture_stmts.pp(short=True)

Both cases produces same result, it could look like this:

== NOTE: duration measures time between 2 captures, it is not actual DB execution time.

== Totally captured 5 statement(s):

  1. 0.00 SELECT FROM person ORDER BY person.id DESC
  2. 0.00 INSERT INTO company_access (alive, allow_empty_cashbag,
     <- 'True+True+False+True+True+False+False+False+False+False+False+False+T
  3. 0.00 SELECT FROM person  WHERE person.id = %(param_1)s
     <- '4'
  4. 0.00 SELECT FROM company_access  WHERE company...
     <- '3'
  5. 0.01 INSERT INTO company_person (packing_model_id, company_access_i
     <- '4+3'

-- By sql command:
    SELECT      3
    INSERT      2

-- By table (top 20):
    PERSON                    2
    COMPANY_ACCESS      2
    COMPANY_PERSON            1

-- By sql command + table (top 20):
    SELECT PERSON                    2
    INSERT COMPANY_ACCESS      1
    SELECT COMPANY_ACCESS      1
    INSERT COMPANY_PERSON            1

One can iterate all statements:

for statement in capture_stmts:
    print(statement.statement)
    print(statement.tst_started)
    print(statement.duration)    # BEWARE: not actual DB execution time, 
                                           Rounded on 2 decimal places.
    print(statement.stmt_repr)   # Dropped list of columns from SELECT
    print(statement.parameters)
    print(statement.executemany) # bool
    print(statement.sql_type)    # BEWARE: do not rely on this
    print(statement.first_table) # BEWARE: do not rely on this