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# Connections to a database

A `Connection` encapsulates access to a database. You then use `cursors` to issue queries against the database.

You can have multple `Connections` open against the same database in the same process, across threads and in other processes.

## Connection class

class `Connection`(filename, flags=SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE, vfs=None, statementcachesize=100)

  This object wraps a sqlite3 pointer.

  Opens the named database. You can use `:memory:` to get a private temporary in-memory database that is not shared with any other connections.

  Parameters:

  - flags – One or more of the open flags orred together
  - vfs – The name of the vfs to use. If `None` then the default vfs will be used.
  - statementcachesize – Use zero to disable the statement cache, or a number larger than the total distinct SQL statements you execute frequently.

  See also

  - `apsw.connection_hooks`
  - Statement Cache
  - Virtual File System (VFS)

  Calls: sqlite3_open_v2

`Connection.``__enter__`() → context

  You can use the database as a context manager as defined in PEP 0343. When you use with a transaction is started. If the block finishes with an exception then the transaction is rolled back, otherwise it is committed. For example:

      with connection:
          connection.cursor().execute("....")
          with connection:
              # nested is supported
              call_function(connection)
              connection.cursor().execute("...")
              with connection as db:
                  # You can also use 'as'
                  call_function2(db)
                  db.cursor().execute("...")

  Behind the scenes the savepoint functionality introduced in SQLite 3.6.8 is used.

`Connection.``__exit__`() → False

  Implements context manager in conjunction with `__enter__()`. Any exception that happened in the with block is raised after commiting or rolling back the savepoint.

`Connection.``backup`(databasename, sourceconnection, sourcedatabasename) → backup

  Opens a backup object. All data will be copied from source database to this database.

  Parameters:

  - databasename – Name of the database. This will be `main` for the main connection and the name you specified for attached databases.
  - sourceconnection – The `Connection` to copy a database from.
  - sourcedatabasename – Name of the database in the source (eg `main`).

  Return type: | `backup`

  See also

  - Backup

  Calls: sqlite3_backup_init

`Connection.``blobopen`(database, table, column, rowid, writeable) → blob

  Opens a blob for incremental I/O.

  Parameters:

  - database –

    Name of the database. This will be `main` for the main connection and the name you specified for attached databases.

  - table – The name of the table
  - column – The name of the column
  - rowid – The id that uniquely identifies the row.
  - writeable – If True then you can read and write the blob. If False then you can only read it.

  Return type: | `blob`

  See also

  - Blob I/O example
  - SQLite row ids

  Calls: sqlite3_blob_open

`Connection.``changes`() → int

  Returns the number of database rows that were changed (or inserted or deleted) by the most recently completed INSERT, UPDATE, or DELETE statement.

  Calls: sqlite3_changes

`Connection.``close`([force=False])

  Closes the database. If there are any outstanding `cursors`, `blobs` or `backups` then they are closed too. It is normally not necessary to call this method as the database is automatically closed when there are no more references. It is ok to call the method multiple times.

  If your user defined functions or collations have direct or indirect references to the Connection then it won’t be automatically garbage collected because of circular referencing that can’t be automatically broken. Calling close will free all those objects and what they reference.

  SQLite is designed to survive power failures at even the most awkward moments. Consequently it doesn’t matter if it is closed when the process is exited, or even if the exit is graceful or abrupt. In the worst case of having a transaction in progress, that transaction will be rolled back by the next program to open the database, reverting the database to a know good state.

  If force is True then any exceptions are ignored.

  Calls: sqlite3_close

`Connection.``collationneeded`(callable)

  callable will be called if a statement requires a collation that hasn’t been registered. Your callable will be passed two parameters. The first is the connection object. The second is the name of the collation. If you have the collation code available then call `Connection.createcollation()`.

  This is useful for creating collations on demand. For example you may include the locale in the collation name, but since there are thousands of locales in popular use it would not be useful to `prereigster` them all. Using `collationneeded()` tells you when you need to register them.

  See also

  - `createcollation()`

  Calls: sqlite3_collation_needed

`Connection.``config`(op[, *args])

  Parameters:

  - op – A configuration operation
  - args – Zero or more arguments as appropriate for op

  Calls: sqlite3_db_config

`Connection.``createaggregatefunction`(name, factory[, numargs=-1])

  Registers an aggregate function. Aggregate functions operate on all the relevant rows such as counting how many there are.

  Parameters:

  - name – The string name of the function. It should be less than 255 characters
  - callable – The function that will be called
  - numargs – How many arguments the function takes, with -1 meaning any number

  When a query starts, the factory will be called and must return a tuple of 3 items:

  > a context object
  >   This can be of any type
  > a step function
  >   This function is called once for each row. The first parameter will be the context object and the remaining parameters will be from the SQL statement. Any value returned will be ignored.
  > a final function
  >   This function is called at the very end with the context object as a parameter. The value returned is set as the return for the function. The final function is always called even if an exception was raised by the step function. This allows you to ensure any resources are cleaned up.

  Note

  You can register the same named function but with different callables and numargs. See `createscalarfunction()` for an example.

  See also

  - Example
  - `createscalarfunction()`

  Calls: sqlite3_create_function_v2

`Connection.``createcollation`(name, callback)

  You can control how SQLite sorts (termed collation) when giving the `COLLATE` term to a SELECT. For example your collation could take into account locale or do numeric sorting.

  The callback will be called with two items. It should return -1 if the first is less then the second, 0 if they are equal, and 1 if first is greater:

      def mycollation(one, two):
          if one < two:
              return -1
          if one == two:
              return 0
          if one > two:
              return 1

  See also

  - Example

  Calls: sqlite3_create_collation_v2

`Connection.``createmodule`(name, datasource)

  Registers a virtual table. See Virtual Tables for details.

  See also

  - Example

  Calls: sqlite3_create_module_v2

`Connection.``createscalarfunction`(name, callable[, numargs=-1])

  Registers a scalar function. Scalar functions operate on one set of paramaters once.

  Parameters:

  - name – The string name of the function. It should be less than 255 characters
  - callable – The function that will be called
  - numargs – How many arguments the function takes, with -1 meaning any number

  Note

  You can register the same named function but with different callable and numargs. For example:

      connection.createscalarfunction("toip", ipv4convert, 4)
      connection.createscalarfunction("toip", ipv6convert, 16)
      connection.createscalarfunction("toip", strconvert, -1)

  The one with the correct numargs will be called and only if that doesn’t exist then the one with negative numargs will be called.

  See also

  - Example
  - `createaggregatefunction()`

  Calls: sqlite3_create_function_v2

`Connection.``cursor`() → Cursor

  Creates a new `Cursor` object on this database.

  Return type: | `Cursor`

`Connection.``db_filename`(name) → String

  Returns the full filename of the named (attached) database. The main database is named “main”.

  Calls: sqlite3_db_filename

`Connection.``enableloadextension`(enable)

  Enables/disables extension loading which is disabled by default.

  Parameters: | enable – If True then extension loading is enabled, else it is disabled.

  See also

  - `loadextension()`

  Calls: sqlite3_enable_load_extension

`Connection.``filecontrol`(dbname, op, pointer) → bool

  Calls the `xFileControl()` method on the Virtual File System (VFS) implementing `file access` for the database.

  Parameters:

  - dbname – The name of the database to affect (eg “main”, “temp”, attached name)
  - op – A numeric code with values less than 100 reserved for SQLite internal use.
  - pointer – A number which is treated as a `void pointer` at the C level.

  Returns: | True or False indicating if the VFS understood the op.

  If you want data returned back then the pointer needs to point to something mutable. Here is an example using ctypes of passing a Python dictionary to `xFileControl()` which can then modify the dictionary to set return values:

      obj={"foo": 1, 2: 3}                 # object we want to pass
      objwrap=ctypes.py_object(obj)        # objwrap must live before and after the call else
                                           # it gets garbage collected
      connection.filecontrol(
               "main",                     # which db
               123,                        # our op code
               ctypes.addressof(objwrap))  # get pointer

  The `xFileControl()` method then looks like this:

      def xFileControl(self, op, pointer):
          if op==123:                      # our op code
              obj=ctypes.py_object.from_address(pointer).value
              # play with obj - you can use id() to verify it is the same
              print obj["foo"]
              obj["result"]="it worked"
              return True
          else:
              # pass to parent/superclass
              return super(MyFile, self).xFileControl(op, pointer)

  This is how you set the chunk size by which the database grows. Do not combine it into one line as the c_int would be garbage collected before the filecontrol call is made:

      chunksize=ctypes.c_int(32768)
      connection.filecontrol("main", apsw.SQLITE_FCNTL_CHUNK_SIZE, ctypes.addressof(chunksize))

  Calls: sqlite3_file_control

`Connection.``filename`

  The filename of the database.

  Calls: sqlite3_db_filename

`Connection.``getautocommit`() → bool

  Returns if the Connection is in auto commit mode (ie not in a transaction).

  Calls: sqlite3_get_autocommit

`Connection.``getexectrace`() → callable or None

  Returns the currently installed (via `setexectrace()`) execution tracer.

  See also

  - Tracing

`Connection.``getrowtrace`() → callable or None

  Returns the currently installed (via `setrowtrace()`) row tracer.

  See also

  - Tracing

`Connection.``interrupt`()

  Causes any pending operations on the database to abort at the earliest opportunity. You can call this from any thread. For example you may have a long running query when the user presses the stop button in your user interface. `InterruptError` will be raised in the query that got interrupted.

  Calls: sqlite3_interrupt

`Connection.``last_insert_rowid`() → int

  Returns the integer key of the most recent insert in the database.

  Calls: sqlite3_last_insert_rowid

`Connection.``limit`(id[, newval]) → int

  If called with one parameter then the current limit for that id is returned. If called with two then the limit is set to newval.

  Parameters:

  - id – One of the runtime limit ids
  - newval – The new limit. This is a 32 bit signed integer even on 64 bit platforms.

  Returns: | The limit in place on entry to the call.

  See also

  - Example

  Calls: sqlite3_limit

`Connection.``loadextension`(filename[, entrypoint])

  Loads filename as an extension

  Parameters:

  - filename – The file to load. This must be Unicode or Unicode compatible
  - entrypoint – The initialization method to call. If this parameter is not supplied then the SQLite default of `sqlite3_extension_init` is used.

  Raises ExtensionLoadingError:
  | If the extension could not be loaded. The exception string includes more details.

  See also

  - `enableloadextension()`

  Calls: sqlite3_load_extension

`Connection.``open_flags`

  The integer flags used to open the database.

`Connection.``open_vfs`

  The string name of the vfs used to open the database.

`Connection.``overloadfunction`(name, nargs)

  Registers a placeholder function so that a virtual table can provide an implementation via `VTTable.FindFunction()`.

  Parameters:

  - name – Function name
  - nargs – How many arguments the function takes

  Due to SQLite ticket #3507 underlying errors will not be returned.

  Calls: sqlite3_overload_function

`Connection.``readonly`(name) → bool

  True or False if the named (attached) database was opened readonly or file permissions don’t allow writing. The main database is named “main”.

  An exception is raised if the database doesn’t exist.

  Calls: sqlite3_db_readonly

`Connection.``setauthorizer`(callable)

  While preparing statements, SQLite will call any defined authorizer to see if a particular action is ok to be part of the statement.

  Typical usage would be if you are running user supplied SQL and want to prevent harmful operations. You should also set the `statementcachesize` to zero.

  The authorizer callback has 5 parameters:

  > - An operation code
  > - A string (or None) dependent on the operation (listed as 3rd)
  > - A string (or None) dependent on the operation (listed as 4th)
  > - A string name of the database (or None)
  > - Name of the innermost trigger or view doing the access (or None)

  The authorizer callback should return one of `SQLITE_OK`, `SQLITE_DENY` or `SQLITE_IGNORE`. (`SQLITE_DENY` is returned if there is an error in your Python code).

  See also

  - Example
  - Statement Cache

  Calls: sqlite3_set_authorizer

`Connection.``setbusyhandler`(callable)

  Sets the busy handler to callable. callable will be called with one integer argument which is the number of prior calls to the busy callback for the same lock. If the busy callback returns something that evaluates to False, then SQLite returns `SQLITE_BUSY` to the calling code.. If the callback returns something that evaluates to True, then SQLite tries to open the table again and the cycle repeats.

  If you previously called `setbusytimeout()` then calling this overrides that.

  See also

  - `Connection.setbusytimeout()`
  - Busy handling

  Calls: sqlite3_busy_handler

`Connection.``setbusytimeout`(millseconds)

  If the database is locked such as when another connection is making changes, SQLite will keep retrying. This sets the maximum amount of time SQLite will keep retrying before giving up. If the database is still busy then `apsw.BusyError` will be returned.

  Parameters: | milliseconds – Maximum thousandths of a second to wait.

  If you previously called `setbusyhandler()` then calling this overrides that.

  See also

  - `Connection.setbusyhandler()`
  - Busy handling

  Calls: sqlite3_busy_timeout

`Connection.``setcommithook`(callable)

  callable will be called just before a commit. It should return zero for the commit to go ahead and non-zero for it to be turned into a rollback. In the case of an exception in your callable, a non-zero (ie rollback) value is returned.

  See also

  - Example

  Calls: sqlite3_commit_hook

`Connection.``setexectrace`(callable)

  callable is called with the cursor, statement and bindings for each `execute()` or `executemany()` on this Connection, unless the `Cursor` installed its own tracer. Your execution tracer can also abort execution of a statement.

  If callable is `None` then any existing execution tracer is removed.

  See also

  - Tracing
  - Row Tracer
  - `Cursor.setexectrace()`

`Connection.``setprofile`(callable)

  Sets a callable which is invoked at the end of execution of each statement and passed the statement string and how long it took to execute. (The execution time is in nanoseconds.) Note that it is called only on completion. If for example you do a `SELECT` and only read the first result, then you won’t reach the end of the statement.

  Calls: sqlite3_profile

`Connection.``setprogresshandler`(callable[, nsteps=20])

  Sets a callable which is invoked every nsteps SQLite inststructions. The callable should return a non-zero value to abort or zero to continue. (If there is an error in your Python callable then non-zero will be returned).

  See also

  - Example

  Calls: sqlite3_progress_handler

`Connection.``setrollbackhook`(callable)

  Sets a callable which is invoked during a rollback. If callable is `None` then any existing rollback hook is removed.

  The callable is called with no parameters and the return value is ignored.

  Calls: sqlite3_rollback_hook

`Connection.``setrowtrace`(callable)

  callable is called with the cursor and row being returned for `cursors` associated with this Connection, unless the Cursor installed its own tracer. You can change the data that is returned or cause the row to be skipped altogether.

  If callable is `None` then any existing row tracer is removed.

  See also

  - Tracing
  - Row Tracer
  - `Cursor.setexectrace()`

`Connection.``setupdatehook`(callable)

  Calls callable whenever a row is updated, deleted or inserted. If callable is `None` then any existing update hook is removed. The update hook cannot make changes to the database while the query is still executing, but can record them for later use or apply them in a different connection.

  The update hook is called with 4 paramaters:

  > type (int)
  >   `SQLITE_INSERT`, `SQLITE_DELETE` or `SQLITE_UPDATE`
  > database name (string)
  >   This is `main` for the database or the name specified in ATTACH
  > table name (string)
  >   The table on which the update happened
  > rowid (64 bit integer)
  >   The affected row

  See also

  - Example

  Calls: sqlite3_update_hook

`Connection.``setwalhook`(callable)

  callable will be called just after data is committed in Write Ahead Logging mode. It should return `SQLITE_OK` or an error code. The callback is called with 3 parameters:

  > - The Connection
  > - The database name (eg “main” or the name of an attached database)
  > - The number of pages in the wal log

  You can pass in None in order to clear an existing hook.

  Calls: sqlite3_wal_hook

`Connection.``sqlite3pointer`() → int

  Returns the underlying sqlite3 * for the connection. This method is useful if there are other C level libraries in the same process and you want them to use the APSW connection handle. The value is returned as a number using `PyLong_FromVoidPtr()` under the hood. You should also ensure that you increment the reference count on the `Connection` for as long as the other libraries are using the pointer. It is also a very good idea to call `sqlitelibversion()` and ensure it is the same as the other libraries.

`Connection.``status`(op, reset=False) -> (int, int)

  Returns current and highwater measurements for the database.

  Parameters:

  - op – A status parameter
  - reset – If True then the highwater is set to the current value

  Returns: | A tuple of current value and highwater value

  See also

  The `status()` example which works in exactly the same way.

  - Status example

  Calls: sqlite3_db_status

`Connection.``totalchanges`() → int

  Returns the total number of database rows that have be modified, inserted, or deleted since the database connection was opened.

  Calls: sqlite3_total_changes

`Connection.``wal_autocheckpoint`(n)

  Sets how often the Write Ahead Logging checkpointing is run.

  Parameters: | n – A number representing the checkpointing interval or zero/negative to disable auto checkpointing.

  Calls: sqlite3_wal_autocheckpoint

`Connection.``wal_checkpoint`(dbname=None, mode=apsw.SQLITE_CHECKPOINT_PASSIVE) -> ( int, int)

  Does a WAL checkpoint. Has no effect if the database(s) are not in WAL mode.

  Parameters:

  - dbname – The name of the database or all databases if None
  - mode – One of the checkpoint modes.

  Returns: | A tuple of the size of the WAL log in frames and the number of frames checkpointed as described in the documentation.

  Calls: sqlite3_wal_checkpoint_v2

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