python query database
The Python DB-API specifies connections and cursors for executing SQL. DBQuery is designed to hide this complexity when it is not needed. Instead it provides a DB and a Query class for executing SQL. DB (or one of its sub classes like SQLiteDB) saves the connection information and provides access to the Query classes which use this to execute the provided SQL.
What is more, if the connection to a database gets lost DBQuery can automatically try to reconnect up to a specified count of retries:
The exact behavior depends on the actual DB implementation for a specific database. In general all configuration parameters are passed to the DB constructor. Usually a connection to the database will not be opened until the first query is made
database, **kwds parameters of the SQLiteDB constructor will be passed on the the SQLite connect function.
Accepts either the DSN string or configuration parameters for the Psqycopg2 connect function as keyword parameters.
Executes a SQL query without being interested in any result. It is the base class for all other queries.
Overwrite _produce_return if you are interested in creating your own class that does something with the cursor that executed the query.
Executes the given SQL then returns the curser for direct access. Use within a context. Exiting the context will close the cursor.
For example perform a fetchone:
> get_first_name_cursor = db.QueryCursor( ... "SELECT first_name FROM users where id=?") >> with get_first_name_cursor(123) as cursor: ... print(cursor.fetchone) ... ('Foo', ) >>
Use this to execute any INSERT, UPDATE and similar queries when the rowcount of the cursor should be returned. It is possible to automatically check the value of the row count by setting the rowcount parameter. If the resulting row count does not match the provided one a ManipulationCheckError will be raised.
This can be used to for example make sure that only one row was updated by a query:
> update_user_name = db.Manipulation( ... "UPDATE users SET first_name=? WHERE id=?", rowcount=1) >> with db: # start a new transaction, does not work with SQLiteDB! ... update_user_name("new_name", 123) # roll back if rowcount != 1 ... 1 >>
Returns the result of fetchall, making it ideal for SELECT queries.
Checks that only one row is returned by the specified query. Returns None otherwise. If the result row contains only one column then only that columns value will be returned:
> get_first_name = db.SelectOne( ... "SELECT first_name FROM users where id=?") >> get_first_name(123) 'Foo' >>
Select rows and precess them in chunks. For this purpose SelectIterator requeires a callback function together with the SQL. This callback will at query time be called with a generator which produces all the rows from the query result, directly streamed from the DB, in blocks of specified size (arraysize).
It is possible to specify additional parameters for the callback function, if needed.
> def callback(row_generator): ... for row in row_generator: ... print(row) ... >> get_first_names = db.SelectIterator( ... 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