Dave Rolsky

NAME

Alzabo::Runtime::Table - Table objects

SYNOPSIS

  my $table = $schema->table('foo');

  my $row = $table->row_by_pk( pk => 1 );

  my $row_cursor =
      $table->rows_where
          ( where =>
            [ Alzabo::Column object, '=', 5 ] );

DESCRIPTION

This object is able to create rows, either by making objects based on existing data or inserting new data to make new rows.

This object also implements a method of lazy column evaluation that can be used to save memory and database wear and tear. Please see the "LAZY COLUMN LOADING" section for details.

INHERITS FROM

Alzabo::Table

METHODS

Methods that return an Alzabo::Runtime::Row object

All of these methods accept the "no_cache" parameter, which will be passed on to Alzabo::Runtime::Row->new.

insert

Inserts the given values into the table. If no value is given for a primary key column and the column is "sequenced" then the primary key will be auto-generated.

It takes the following parameters:

  • values => $hashref

    The hashref contains column names and values for the new row. This parameter is optional. If no values are specified, then the default values will be used.

This methods return a new Alzabo::Runtime::Row object.

Throws: Alzabo::Exception::Logic, Alzabo::Exception::NotNullable, Alzabo::Exception::Params

row_by_pk

The primary key can be either a simple scalar, as when the table has a single primary key, or a hash reference of column names to primary key values, for multi-column primary keys.

It takes the following parameters:

  • pk => $pk_val or \%pk_val

It returns a new Alzabo::Runtime::Row object. If no rows in the database match the value(s) given then an empty list or undef will be returned (for list or scalar context).

Throws: Alzabo::Exception::Logic, Alzabo::Exception::Params

row_by_id

This method is useful for regenerating a row that has been saved by reference to its id (returned by the Alzabo::Runtime::Row->id method). This may be more convenient than saving a multi-column primary key when trying to maintain state in a web app, for example.

Throws: Alzabo::Exception::Logic, Alzabo::Exception::Params

This method takes a single parameter, "row_id", which is the string representation of a row's id, as returned by the Alzabo::Runtime::Row->id_as_string() method.

It returns a new Alzabo::Runtime::Row object. If no rows in the database match the value(s) given then an empty list or undef will be returned (for list or scalar context).

Insert Handles

If you are going to be inserting many rows at once, it is more efficient to create an insert handle and re-use that. This is similar to how DBI allows you to create statement handles and execute them multiple times.

insert_handle

This method takes the following parameters:

  • columns => $arrayref

    This should be an array reference containing zero or more Alzabo::Runtime::Column objects.

    If it is empty, or not provided, then defaults will be used for all columns.

  • values => $hashref

    This is used to specify values that will be the same for each row. These can be actual values or SQL functions.

The return value of this method is an Alzabo::Runtime::InsertHandle object. This object has a single method, insert(). See the Alzabo::Runtime::InsertHandle docs for details.

Throws: Alzabo::Exception::NotNullable, Alzabo::Exception::Params

Common Parameters

A number of methods in this clas take the same parameters. These are documented below.

  • where => <see below>

    This parameter can take a variety of values. The most basic "where" parameter is a single array reference of this form:

      [ Alzabo::Column object or SQL function,
        $comparison,
        $value or Alzabo::Column object ]

    The $comparison should be a string containing a SQL operator such as >, =, or IN.

    The parameter can also be an array reference containing many such arrays:

     [
       [ Alzabo::Column object or SQL function,
         $comparison,
         $value or Alzabo::Column object ],
       [ Alzabo::Column object or SQL function,
         $comparison,
         $value or Alzabo::Column object ],
       ...
     ]

    If the comparison is "BETWEEN", then it should be followed by two values. If it is "IN" or "NOT IN", then it should be followed by a list of one or more values.

    By default, each clause represented by an array reference is joined together with an 'AND'. However, you can put the string 'or' between two array references to cause them to be joined with an 'OR', such as:

     [ [ $foo_col, '=', 5 ],
       'or',
       [ $foo_col, '>', 10 ] ]

    which would generate SQL something like:

     WHERE foo = 5 OR foo > 10

    If you want to be explicit, you can also use the string 'and'.

    If you need to group conditionals you can use '(' and ')' strings in between array references representing a conditional. For example:

     [ [ $foo_col, '=', 5 ],
       '(',
         [ $foo_col, '>', 10 ]
         'or',
         [ $bar_col, '<', 50, ')' ],
       ')' ]

    which would generate SQL something like:

     WHERE foo = 5 AND ( foo > 10 OR bar < 50 )

    Make sure that your parentheses balance out or an exception will be thrown.

    You can also use the SQL functions (Using SQL functions) exported from the SQLMaker subclass you are using. For example:

     [ LENGTH($foo_col), '<', 10 ]

    would generate something like:

     WHERE LENGTH(foo) < 10
  • order_by => see below

    This parameter can take one of two different values. The simplest form is to just give it a single column object or SQL function. Alternatively, you can give it an array reference to a list of column objects, SQL functions and strings like this:

      order_by => [ $col1, COUNT('*'), $col2, 'DESC', $col3, 'ASC' ]

    It is important to note that you cannot simply use any arbitrary SQL function as part of your order by clause. You need to use a function that is exactly the same as one that was given as part of the "select" parameter.

  • group_by => see below

    This parameter can take either a single column object or an array of column objects.

  • having => same as "where"

    This parameter is specified in the same way as the "where" parameter.

  • limit => $limit or [ $limit, $offset ]

    For databases that support LIMIT clauses, this incorporates such a clause into the SQL.

    For databases that don't, the limit will be implemented programatically as rows are being requested. If an offset is given, this will be the number of rows skipped in the result set before the first one is returned.

Methods that return an Alzabo::Runtime::RowCursor object

The rows_where() and all_rows() methods both return an Alzabo::Runtime::RowCursor object representing the results of the query. This is the case even for queries that end up returning one or zero rows, because Alzabo cannot know in advance how many rows these queries will return.

rows_where

This method provides a simple way to retrieve a row cursor based on one or more colum values.

It takes the following parameters, all of which were described in the Common Parameters section.

  • where

  • order_by

  • limit

It returns n Alzabo::Runtime::RowCursor object representing the query.

Throws: Alzabo::Exception::Logic, Alzabo::Exception::Params

all_rows

This method simply returns all the rows in the table.

It takes the following parameters:

  • order_by

  • limit

It returns an Alzabo::Runtime::RowCursor object representing the query.

Throws: Alzabo::Exception::Logic, Alzabo::Exception::Params

one_row

This method takes the exact same parameters as the rows_where() method but instead of returning a cursor, it returns a single row. This row represents the first row returned by the database.

Throws: Alzabo::Exception::Logic, Alzabo::Exception::Params

potential_row

This method is used to create a new Alzabo::Runtime::Row object, in the "potential" state.

It takes the following parameters.

  • values => \%values

    This should be a hash reference containing column names, just as is given to insert().

    It is ok to omit columns that are normally not nullable, but they cannot be explicitly set to null.

    Any values given will be set in the new potential row object. If a column has a default, and a value for that column is not given, then the default will be used.

    Unlike the "insert" in insert()\ method, you cannot use SQL functions as values here.

Throws: Alzabo::Exception::Logic, Alzabo::Exception::Params

Other Methods

This method returns a count of the rows in the table. It takes the following parameters:

row_count

  • where

Throws: Alzabo::Exception::Logic, Alzabo::Exception::Params

function and select

These two methods differ only in their return values.

They both take the following parameters:

  • select => $function or [ scalars, SQL functions and/or Alzabo::Column objects ]

    If you pass an array reference for this parameter, it may contain scalars, SQL functions, or column objects. For example:

      $table->function( select =>
                        [ 1,
                          $foo->column('name'),
                          LENGTH( $foo->column('name') ) ] );

    This is equivalent to the following SQL:

      SELECT 1, foo.name, LENGTH( foo.name )
        FROM foo
  • where

  • order_by

  • group_by

  • limit

This method is used to call arbitrary SQL functions such as 'AVG' or 'MAX', or to select arbitrary column data. The function (or functions) should be the return values from the functions exported by the SQLMaker subclass that you are using. Please see Using SQL functions for more details.

Throws: Alzabo::Exception::Logic, Alzabo::Exception::Params

function() return values

The return value of this method is highly context sensitive.

If you only requested a single element in your "select" parameter, such as "DISTINCT(foo)", then it returns the first value in scalar context and all the values as an array in list context.

If you requested multiple functions such as "AVG(foo), MAX(foo)", then it returns a single array reference, the first row of values, in scalar context and a list of array references in list context.

select() return values

This method always returns a new Alzabo::DriverStatement object containing the results of the query. This object has an interface very similar to the Alzabo cursor interface, and has methods such as next(), next_as_hash(), etc.

alias

This returns an object which can be used in joins to allow a particular table to be involved in the join under multiple aliases. This allows for self-joins as well as more complex joins involving multiple aliases to a given table.

The object returned by this method is more or less identical to a table object in terms of the methods it supports. This includes methods that were generated by Alzabo::MethodMaker.

However, this object should not be used outside the context of a join query because the results will be unpredictable. In addition, the column objects that the aliased table object returns should also not be used outside of the context of a join.

LAZY COLUMN LOADING

This concept was taken directly from Michael Schwern's Class::DBI module (credit where it is due).

By default, Alzabo::Runtime::Row objects load all data from the database except blob type columns (columns with an unbounded length). This data is stored internally in the object after being fetched.

If you want to change what data is prefetched, there are two methods you can use.

The first method, set_prefetch(), allows you to specify a list of columns to be fetched immediately after object creation. These should be columns that you expect to use extremely frequently.

The second method, add_group(), allows you to group columns together. If you attempt to fetch one of these columns, then all the columns in the group will be fetched. This is useful in cases where you don't often want certain data, but when you do you need several related pieces.

set_prefetch (Alzabo::Column objects)

Given a list of column objects, this makes sure that all Alzabo::Runtime::Row objects fetch this data as soon as they are created.

NOTE: It is pointless (though not an error) to give primary key column here as these are always prefetched (in a sense).

Throws: Alzabo::Exception::Params

add_group (Alzabo::Column objects)

Given a list of Alzabo::Column objects, this method creates a group containing these columns. This means that if any column in the group is fetched from the database, then they will all be fetched. Otherwise column are always fetched singly. Currently, a column cannot be part of more than one group.

NOTE: It is pointless to include a column that was given to the set_prefetch() method in a group here, as it always fetched as soon as possible.

Throws: Alzabo::Exception::Params

prefetch

This method primarily exists for use by the Alzabo::Runtime::Row class.

It returns a list of column names (not objects) that should be prefetched.

group_by_column ($column_name)

This method primarily exists for use by the Alzabo::Runtime::Row class.

It returns a list of column names representing the group that the given column is part of. If the column is not part of a group, only the name passed in is returned.

AUTHOR

Dave Rolsky, <autarch@urth.org>




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