NAME

Catmandu::Store::DBI::Bag - implementation of a Catmandu::Bag for DBI

SYNOPSIS

            

              
              
my $store = Catmandu::Store::DBI->new(
    data_source => "dbi:SQLite:dbname=/tmp/test.db",
    bags => {
        data => {
            mapping => {
                _id => {
                    column => 'id',
                    type => 'string',
                    index => 1,
                    unique => 1
                },
                author => {
                    type => 'string'
                },
                subject => {
                    type => 'string',
                },
                _data => {
                    column => 'data',
                    type => 'binary',
                    serialize => 'all'
                }
            }
        }
    }
);
my $bag = $store->bag('data');
#SELECT
{
    #SELECT * FROM DATA WHERE author = 'Nicolas'
    my $iterator = $bag->select( author => 'Nicolas' );
}
#CHAINED SELECT
{
    #SELECT * FROM DATA WHERE author = 'Nicolas' AND subject = 'ICT'
    my $iterator = $bag->select( author => 'Nicolas' )->select( subject => 'ICT' );
}
#COUNT
{
    #SELECT * FROM DATA WHERE author = 'Nicolas'
    my $iterator = $bag->select( author => 'Nicolas' );
    #SELECT COUNT(*) FROM ( SELECT * FROM DATA WHERE author = 'Nicolas' )
    my $count = $iterator->count();
}
#DETECT
{
    #SELECT * FROM DATA WHERE author = 'Nicolas' AND subject = 'ICT' LIMIT 1
    my $record = $bag->select( author => 'Nicolas' )->detect( subject => 'ICT' );
}
#NOTES
{
    #This creates an iterator with a specialized SQL query:
    #SELECT * FROM DATA WHERE author = 'Nicolas'
    my $iterator = $bag->select( author => 'Nicolas' );
    #But this does not
    my $iterator2 = $iterator->select( title => "Hello world" );
    #'title' does not have a corresponding table column, so it falls back to the default implementation,
    #and loops over every record.
}
{
    #this is faster..
    my $iterator = $bag->select( author => 'Nicolas' )->select( title => 'Hello world');
    #..than
    my $iterator2 = $bag->select( title => 'Hello world' )->select( author => 'Nicolas' );
    #reason:
    #   the select statement of $iterator creates a specialized query, and so reduces the amount of records to loop over.
    #   $iterator is a L<Catmandu::Store::DBI::Iterator>.
    #   the select statement of $iterator2 does not have a specialized query, so it's a generic L<Catmandu::Iterator>.
    #   the second select statement of $iterator2 receives this generic object as its source, and can only loop over its records.
}
            
          

DESCRIPTION

Catmandu::Store::DBI::Bag provides some method overrides specific for DBI interfaces, to make querying more efficient.

METHODS

store_with_table

Equivalent to the store accessor, but ensures that the table for this bag exists.

select($key => $val)

Overrides equivalent method in Catmandu::Bag.

Either returns a generic Catmandu::Iterator or a more efficient Catmandu::Store::DBI::Iterator.

Expect the following behaviour:

• the key has a corresponding table column configured

  a SQL where clause is created in the background:

  .. WHERE $key = $val

  Chained select statements with existing table columns result in a combined where clause:

  
              
  
                
                
  .. WHERE $key1 = $val1 AND $key2 = $val2 ..
              
            

  The returned object is a Catmandu::Store::DBI::Iterator, instead of the generic Catmandu::Iterator.

• the key does not have a corresponding table column configured

  The returned object is a generic Catmandu::Iterator.

  This iterator can only loop over the records provided by the previous Catmandu::Iterable.

A few important notes:

• A select statement only results in a Catmandu::Store::DBI::Iterator, when it has a mapped key, and the previous iterator is either a Catmandu::Store::DBI::Bag or a Catmandu::Store::DBI::Iterator.

• As soon as the returned object is a generic Catmandu::Iterator, any following select statement with mapped columns will not make a more efficient Catmandu::Store::DBI::Iterator.

In order to make your chained statements efficient, do the following:

• create indexes on the table columns

• put select statements with mapped keys in front, and those with non mapped keys at the end.

To configure table columns, see Catmandu::Store::DBI.

detect($key => $val)

Overrides equivalent method in Catmandu::Bag.

Also returns first record where $key matches $val.

Works like the select method above, but adds the SQL statement 'LIMIT 1' to the current SQL query in the background.

first()

Overrides equivalent method in Catmandu::Bag.

Also returns first record using the current iterator.

The parent method uses a generator, but fetches only one record.

This method adds the SQL statement 'LIMIT 1' to the current SQL query.

count()

Overrides equivalent method in Catmandu::Bag.

When the source is a Catmandu::Store::DBI::Bag, or a Catmandu::Store::DBI::Iterator, a specialized SQL query is created:

            

              
              
SELECT COUNT(*) FROM TABLE WHERE (..)
            
          

The select statement of the source is between the parenthesises.

cpanm Catmandu::DBI

perl -MCPAN -e shell
install Catmandu::DBI