NAME
DBD::Mock - Mock database driver for testing
SYNOPSIS
use DBI;
# ...connect as normal, using 'Mock' as your driver name
my $dbh = DBI->connect( 'DBI:Mock:', '', '' )
|| die "Cannot create handle: $DBI::errstr\n";
# ...create a statement handle as normal and execute with parameters
my $sth = $dbh->prepare( 'SELECT this, that FROM foo WHERE id = ?' );
$sth->execute( 15 );
# Now query the statement handle as to what has been done with it
my $params = $sth->{mock_params};
print "Used statement: ", $sth->{mock_statement}, "\n",
"Bound parameters: ", join( ', ', @{ $params } ), "\n";DESCRIPTION
Purpose
Testing with databases can be tricky. If you are developing a system married to a single database then you can make some assumptions about your environment and ask the user to provide relevant connection information. But if you need to test a framework that uses DBI, particularly a framework that uses different types of persistence schemes, then it may be more useful to simply verify what the framework is trying to do -- ensure the right SQL is generated and that the correct parameters are bound. DBD::Mock makes it easy to just modify your configuration (presumably held outside your code) and just use it instead of DBD::Foo (like DBD::Pg or DBD::mysql) in your framework.
There is no distinct area where using this module makes sense. (Some people may successfully argue that this is a solution looking for a problem...) Indeed, if you can assume your users have something like DBD::AnyData or DBD::SQLite or if you do not mind creating a dependency on them then it makes far more sense to use these legitimate driver implementations and test your application in the real world -- at least as much of the real world as you can create in your tests...
And if your database handle exists as a package variable or something else easily replaced at test-time then it may make more sense to use Test::MockObject to create a fully dynamic handle. There is an excellent article by chromatic about using Test::MockObject in this and other ways, strongly recommended. (See "SEE ALSO" for a link)
How does it work?
DBD::Mock comprises a set of classes used by DBI to implement a database driver. But instead of connecting to a datasource and manipulating data found there it tracks all the calls made to the database handle and any created statement handles. You can then inspect them to ensure what you wanted to happen actually happened. For instance, say you have a configuration file with your database connection information:
[DBI]
dsn = DBI:Pg:dbname=myapp
user = foo
password = barAnd this file is read in at process startup and the handle stored for other procedures to use:
package ObjectDirectory;
my ( $DBH );
sub run_at_startup {
my ( $class, $config ) = @_;
$config ||= read_configuration( ... );
my $dsn = $config->{DBI}{dsn};
my $user = $config->{DBI}{user};
my $pass = $config->{DBI}{password};
$DBH = DBI->connect( $dsn, $user, $pass ) || die ...;
}
sub get_database_handle {
return $DBH;
}A procedure might use it like this (ignoring any error handling for the moment):
package My::UserActions;
sub fetch_user {
my ( $class, $login ) = @_;
my $dbh = ObjectDirectory->get_database_handle;
my $sql = q{
SELECT login_name, first_name, last_name, creation_date, num_logins
FROM users
WHERE login_name = ?
};
my $sth = $dbh->prepare( $sql );
$sth->execute( $login );
my $row = $sth->fetchrow_arrayref;
return ( $row ) ? User->new( $row ) : undef;
}So for the purposes of our tests we just want to ensure that:
The right SQL is being executed
The right parameters are bound
Assume whether the SQL actually works or not is irrelevant for this test :-)
To do that our test might look like:
my $config = ObjectDirectory->read_configuration( ... );
$config->{DBI}{dsn} = 'DBI:Mock:';
ObjectDirectory->run_at_startup( $config );
my $login_name = 'foobar';
my $user = My::UserActions->fetch_user( $login_name );
# Get the handle from ObjectDirectory; this is the same handle used
# in the 'fetch_user()' procedure above
my $dbh = ObjectDirectory->get_database_handle();
# Ask the database handle for the history of all statements executed
# against it
my $history = $dbh->{mock_all_history};
# Now query that history record to see if our expectations match
# reality
is( scalar @{ $history }, 1,
'Correct number of statements executed' );
my $login_st = $history->[0];
like( $login_st->statement, qr/SELECT login_name.*FROM users WHERE login_name = ?/sm,
'Correct statement generated' );
my $params = $login_st->bound_params;
is( scalar @{ $params }, 1,
'Correct number of parameters bound' );
is( $params->[0], $login_name,
'Correct value for parameter 1' );
# Reset the handle for future operations
$dbh->{mock_clear_history} = 1;The list of properties and what they return is listed below. But in an overall view:
A database handle contains the history of all statements created against it. Other properties set for the handle (e.g., 'PrintError', 'RaiseError') are left alone and can be queried as normal, but they do not affect anything. (A future feature may track the sequence/history of these assignments but if there is no demand it probably will not get implemented.)
A statement handle contains the statement it was prepared with plus all bound parameters or parameters passed via
execute(). It can also contain predefined results for the statement handle to 'fetch', track how many fetches were called and what its current record is.
A Word of Warning
This may be an incredibly naive implementation of a DBD. But it works for me...
PROPERTIES
Since this is a normal DBI statement handle we need to expose our tracking information as properties (accessed like a hash) rather than methods.
Database Handle Properties
mock_all_history
Returns an array reference with all history (a.k.a. DBD::Mock::StatementTrack) objects created against the database handle in the order they were created. Each history object can then report information about the SQL statement used to create it, the bound parameters, etc..
mock_clear_history
If set to a true value all previous statement history operations will be erased. This includes the history of currently open handles, so if you do something like:
my $dbh = get_handle( ... );
my $sth = $dbh->prepare( ... );
$dbh->{mock_clear_history} = 1;
$sth->execute( 'Foo' );You will have no way to learn from the database handle that the statement parameter 'Foo' was bound.
This is useful mainly to ensure you can isolate the statement histories from each other. A typical sequence will look like:
set handle to framework
perform operations
analyze mock database handle
reset mock database handle history
perform more operations
analyze mock database handle
reset mock database handle history
...Statement Handle Properties
mock_statement
The SQL statement this statement handle was prepared with. So if the handle were created with:
my $sth = $dbh->prepare( 'SELECT * FROM foo' );This would return:
SELECT * FROM fooThe original statement is unmodified so if you are checking against it in tests you may want to use a regex rather than a straight equality check. (However if you use a phrasebook to store your SQL externally you are a step ahead...)
mock_fields
Fields used by the statement. As said elsewhere we do no analysis or parsing to find these, you need to define them beforehand. That said, you do not actually need this very often.
Note that this returns the same thing as the normal statement property 'FIELD'.
mock_params
Returns an arrayref of parameters bound to this statement in the order specified by the bind type. For instance, if you created and stocked a handle with:
my $sth = $dbh->prepare( 'SELECT * FROM foo WHERE id = ? AND is_active = ?' );
$sth->bind_param( 2, 'yes' );
$sth->bind_param( 1, 7783 );This would return:
[ 7738, 'yes' ]The same result will occur if you pass the parameters via execute() instead:
my $sth = $dbh->prepare( 'SELECT * FROM foo WHERE id = ? AND is_active = ?' );
$sth->execute( 7783, 'yes' );mock_records
An arrayref of arrayrefs representing the records the mock statement was stocked with.
mock_num_records
Number of records the mock statement was stocked with; if never stocked it is still 0. (Some weirdos might expect undef...)
mock_current_record_num
Current record the statement is on; returns 0 in the instances when you have not yet called execute() and if you have not yet called a fetch method after the execute.
mock_is_executed
Whether execute() has been called against the statement handle. Returns 'yes' if so, 'no' if not.
mock_is_finished
Whether finish() has been called against the statement handle. Returns 'yes' if so, 'no' if not.
mock_is_depleted
Returns 'yes' if all the records in the recordset have been returned. If no fetch() was executed against the statement, or If no return data was set this will return 'no'.
mock_my_history
Returns a DBD::Mock::StatementTrack object which tracks the actions performed by this statement handle. Most of the actions are separately available from the properties listed above, so you should never need this.
THE DBD::Mock::StatementTrack OBJECT
Under the hood this module does most of the work with a DBD::Mock::StatementTrack object. This is most useful when you are reviewing multiple statements at a time, otherwise you might want to use the mock_* statement handle attributes instead.
Methods
new( %params )
Takes the following parameters:
return_data: Arrayref of return data records
fields: Arrayref of field names
bound_params: Arrayref of bound parameters
is_executed: Boolean (as 'yes' or 'no') indicating whether the statement has been executed.
is_finished: Boolean (as 'yes' or 'no') indicating whether the statement has been finished.
statement (Statement attribute 'mock_statement')
Gets/sets the SQL statement used.
fields (Statement attribute 'mock_fields')
Gets/sets the fields to use for this statement.
bound_params (Statement attribute 'mock_params')
Gets/set the bound parameters to use for this statement.
return_data (Statement attribute 'mock_records')
Gets/sets the data to return when asked (that is, when someone calls 'fetch' on the statement handle).
current_record_num (Statement attribute 'mock_current_record_num')
Gets/sets the current record number.
is_executed( $yes_or_no ) (Statement attribute 'mock_is_executed')
Sets the state of the tracker 'executed' flag.
is_finished( $yes_or_no ) (Statement attribute 'mock_is_finished')
If set to 'yes' tells the tracker that the statement is finished. This resets the current record number to '0' and clears out the array ref of returned records.
is_depleted() (Statement attribute 'mock_is_depleted')
Returns true if the current record number is greater than the number of records set to return.
num_fields
Returns the number of fields set in the 'fields' parameter.
num_params
Returns the number of parameters set in the 'bound_params' parameter.
bound_param( $param_num, $value )
Sets bound parameter $param_num to $value. Returns the arrayref of currently-set bound parameters. This corresponds to the 'bind_param' statement handle call.
bound_param_trailing( @params )
Pushes @params onto the list of already-set bound parameters.
mark_executed()
Tells the tracker that the statement has been executed and resets the current record number to '0'.
next_record()
If the statement has been depleted (all records returned) returns undef; otherwise it gets the current recordfor returning, increments the current record number and returns the current record.
to_string()
Tries to give an decent depiction of the object state for use in debugging.
SEE ALSO
DBD::NullP, which provided a good starting point
Test::MockObject, which provided the approach
Test::MockObject article - http://www.perl.com/pub/a/2002/07/10/tmo.html
COPYRIGHT
Copyright (c) 2004 Chris Winters. All rights reserved.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
AUTHORS
Chris Winters <chris@cwinters.com>