Declare the database table for which this class is defined, using the protected variable $_name. This is a string, and must contain the name of the table spelled as it appears in the database.

If you don't specify the table name, it defaults to the name of the class. If you rely on this default, the class name must match the spelling of the table name as it appears in the database.

You can also declare the schema for the table, either with the protected variable $_schema, or with the schema prepended to the table name in the $_name property. Any schema specified with the $_name property takes precedence over a schema specified with the $_schema property. In some RDBMS brands, the term for schema is "database" or "tablespace," but it is used similarly.

The schema and table names may also be specified via constructor configuration directives, which override any default values specified with the $_name and $_schema properties. A schema specification given with the name directive overrides any value provided with the schema option.

If you don't specify the schema name, it defaults to the schema to which your database adapter instance is connected.

Every table must have a primary key. You can declare the column for the primary key using the protected variable $_primary. This is either a string that names the single column for the primary key, or else it is an array of column names if your primary key is a compound key.

If you don't specify the primary key, Zend_Db_Table_Abstract tries to discover the primary key based on the information provided by the describeTable()´ method.

Note: Every table class must know which columns can be used to address rows uniquely. If no primary key columns are specified in the table class definition or the table constructor arguments, or discovered in the table metadata provided by describeTable(), then the table cannot be used with Zend_Db_Table.

When you create an instance of a Table class, the constructor calls a set of protected methods that initialize metadata for the table. You can extend any of these methods to define metadata explicitly. Remember to call the method of the same name in the parent class at the end of your method.

The setup methods you can override are the following:

• _setupDatabaseAdapter() checks that an adapter has been provided; gets a default adapter from the registry if needed. By overriding this method, you can set a database adapter from some other source.

• _setupTableName() defaults the table name to the name of the class. By overriding this method, you can set the table name before this default behavior runs.

• _setupMetadata() sets the schema if the table name contains the pattern "schema.table"; calls describeTable() to get metadata information; defaults the $_cols array to the columns reported by describeTable(). By overriding this method, you can specify the columns.

• _setupPrimaryKey() defaults the primary key columns to those reported by describeTable(); checks that the primary key columns are included in the $_cols array. By overriding this method, you can specify the primary key columns.

If application-specific logic needs to be initialized when a Table class is constructed, you can select to move your tasks to the init() method, which is called after all Table metadata has been processed. This is recommended over the __construct() method if you do not need to alter the metadata in any programmatic way.

The first way to provide a database adapter to a Table class is by passing it as an object of type Zend_Db_Adapter_Abstract in the options array, identified by the key 'db'.

The second way to provide a database adapter to a Table class is by declaring an object of type Zend_Db_Adapter_Abstract to be a default database adapter for all subsequent instances of Tables in your application. You can do this with the static method Zend_Db_Table_Abstract::setDefaultAdapter(). The argument is an object of type Zend_Db_Adapter_Abstract.

It can be convenient to create the database adapter object in a central place of your application, such as the bootstrap, and then store it as the default adapter. This gives you a means to ensure that the adapter instance is the same throughout your application. However, setting a default adapter is limited to a single adapter instance.

The third way to provide a database adapter to a Table class is by passing a string in the options array, also identified by the 'db' key. The string is used as a key to the static Zend_Registry instance, where the entry at that key is an object of type Zend_Db_Adapter_Abstract.

Like setting the default adapter, this gives you the means to ensure that the same adapter instance is used throughout your application. Using the registry is more flexible, because you can store more than one adapter instance. A given adapter instance is specific to a certain RDBMS brand and database instance. If your application needs access to multiple databases or even multiple database brands, then you need to use multiple adapters.

An auto-incrementing primary key generates a unique integer value for you if you omit the primary key column from your SQL INSERT statement.

In Zend_Db_Table_Abstract, if you define the protected variable $_sequence to be the Boolean value TRUE, then the class assumes that the table has an auto-incrementing primary key.

MySQL, Microsoft SQL Server, and SQLite are examples of RDBMS brands that support auto-incrementing primary keys.

PostgreSQL has a SERIAL notation that implicitly defines a sequence based on the table and column name, and uses the sequence to generate key values for new rows. IBM DB2 has an IDENTITY notation that works similarly. If you use either of these notations, treat your Zend_Db_Table class as having an auto-incrementing column with respect to declaring the $_sequence member as TRUE.

A sequence is a database object that generates a unique value, which can be used as a primary key value in one or more tables of the database.

If you define $_sequence to be a string, then Zend_Db_Table_Abstract assumes the string to name a sequence object in the database. The sequence is invoked to generate a new value, and this value is used in the INSERT operation.

Oracle, PostgreSQL, and IBM DB2 are examples of RDBMS brands that support sequence objects in the database.

PostgreSQL and IBM DB2 also have syntax that defines sequences implicitly and associated with columns. If you use this notation, treat the table as having an auto-incrementing key column. Define the sequence name as a string only in cases where you would invoke the sequence explicitly to get the next key value.

Some tables have a natural key. This means that the key is not automatically generated by the table or by a sequence. You must specify the value for the primary key in this case.

If you define the $_sequence to be the Boolean value FALSE, then Zend_Db_Table_Abstract assumes that the table has a natural primary key. You must provide values for the primary key columns in the array of data to the insert() method, or else this method throws a Zend_Db_Table_Exception.

Note: All RDBMS brands support tables with natural keys. Examples of tables that are often declared as having natural keys are lookup tables, intersection tables in many-to-many relationships, or most tables with compound primary keys.

The Zend_Db_Table_Select object is an extension of the Zend_Db_Select object that applies specific restrictions to a query. The enhancements and restrictions are:

• You can elect to return a subset of columns within a fetchRow or fetchAll query. This can provide optimization benefits where returning a large set of results for all columns is not desirable.

• You can specify columns that evaluate expressions from within the selected table. However this will mean that the returned row or rowset will be readOnly and cannot be used for save() operations. A Zend_Db_Table_Row with readOnly status will throw an exception if a save() operation is attempted.

• You can allow JOIN clauses on a select to allow multi-table lookups.

• You can not specify columns from a JOINed tabled to be returned in a row or rowset. Doing so will trigger a PHP error. This was done to ensure the integrity of the Zend_Db_Table is retained. i.e. A Zend_Db_Table_Row should only reference columns derived from its parent table.

Fluent interfaces are implemented across the component, so this can be rewritten this in a more abbreviated form.

You can query for a set of rows using any criteria other than the primary key values, using the fetchAll() method of the Table class. This method returns an object of type Zend_Db_Table_Rowset_Abstract.

You may also pass sorting criteria in an ORDER BY clause, as well as count and offset integer values, used to make the query return a specific subset of rows. These values are used in a LIMIT clause, or in equivalent logic for RDBMS brands that do not support the LIMIT syntax.

All of the arguments above are optional. If you omit the ORDER clause, the result set includes rows from the table in an unpredictable order. If no LIMIT clause is set, you retrieve every row in the table that matches the WHERE clause.

For more specific and optimized requests, you may wish to limit the number of columns returned in a row or rowset. This can be achieved by passing a FROM clause to the select object. The first argument in the FROM clause is identical to that of a Zend_Db_Select object with the addition of being able to pass an instance of Zend_Db_Table_Abstract and have it automatically determine the table name.

You can also specify expressions within a FROM clause and have these returned as a readOnly row or rowset. In this example we will return a rows from the bugs table that show an aggregate of the number of new bugs reported by individuals. Note the GROUP clause. The 'count' column will be made available to the row for evaluation and can be accessed as if it were part of the schema.

You can also use a lookup as part of your query to further refine your fetch operations. In this example the accounts table is queried as part of a search for all new bugs reported by 'Bob'.

The Zend_Db_Table_Select is primarily used to constrain and validate so that it may enforce the criteria for a legal SELECT query. However there may be certain cases where you require the flexibility of the Zend_Db_Table_Row component and do not require a writable or deletable row. for this specific user case, it is possible to retrieve a row or rowset by passing a FALSE value to setIntegrityCheck(). The resulting row or rowset will be returned as a 'locked' row (meaning the save(), delete() and any field-setting methods will throw an exception).

To take metadata caching a step further, you can also choose to hardcode metadata. In this particular case, however, any changes to the table schema will require a change in your code. As such, it is only recommended for those who are optimizing for production usage.

The metadata structure is as follows:

An easy way to get the appropriate values is to use the metadata cache, and then to deserialize values stored in the cache.

You can disable this optimization by turning of the metadataCacheInClass flag:

The flag is enabled by default, which ensures that the $_metadata array is only populated once per instance.

By default, methods of the Table class return a Rowset in instances of the concrete class Zend_Db_Table_Rowset, and Rowsets contain a collection of instances of the concrete class Zend_Db_Table_Row You can specify an alternative class to use for either of these, but they must be classes that extend Zend_Db_Table_Rowset_Abstract and Zend_Db_Table_Row_Abstract, respectively.

You can specify Row and Rowset classes using the Table constructor's options array, in keys 'rowClass' and 'rowsetClass' respectively. Specify the names of the classes using strings.

You can change the classes by specifying them with the setRowClass() and setRowsetClass() methods. This applies to rows and rowsets created subsequently; it does not change the class of any row or rowset objects you have created previously.

For more information on the Row and Rowset classes, see this chapter and this one.

You can override the insert() and update() methods in your Table class. This gives you the opportunity to implement custom code that is executed before performing the database operation. Be sure to call the parent class method when you are done.

You can also override the delete() method.

You can implement custom query methods in your Table class, if you have frequent need to do queries against this table with specific criteria. Most queries can be written using fetchAll(), but this requires that you duplicate code to form the query conditions if you need to run the query in several places in your application. Therefore it can be convenient to implement a method in the Table class to perform frequently-used queries against this table.

Some people prefer that the table class name match a table name in the RDBMS by using a string transformation called inflection.

For example, if your table class name is "BugsProducts", it would match the physical table in the database called "bugs_products", if you omit the explicit declaration of the $_name class property. In this inflection mapping, the class name spelled in "CamelCase" format would be transformed to lower case, and words are separated with an underscore.

You can specify the database table name independently from the class name by declaring the table name with the $_name class property in each of your table classes.

Zend_Db_Table_Abstract performs no inflection to map the class name to the table name. If you omit the declaration of $_name in your table class, the class maps to a database table that matches the spelling of the class name exactly.

It is inappropriate to transform identifiers from the database, because this can lead to ambiguity or make some identifiers inaccessible. Using the SQL identifiers exactly as they appear in the database makes Zend_Db_Table_Abstract both simpler and more flexible.

If you prefer to use inflection, then you must implement the transformation yourself, by overriding the _setupTableName() method in your Table classes. One way to do this is to define an abstract class that extends Zend_Db_Table_Abstract, and then the rest of your tables extend your new abstract class.

You are responsible for writing the functions to perform inflection transformation. Zend Framework does not provide such a function.