Database API

Database API overview

The Drupal 7 Database API provides a standard, vendor-agnostic abstraction layer for accessing database servers.

General concepts

The Drupal database layer is built on top of the PHP's PDO library. PDO provides a unified, object-oriented API for accessing different

Database configuration

The primary means of defining a database connection is via the $databases array in settings.php. As its name suggests, $databases allows

Static queries

Use static queries for simple SELECT statements that don't need to be altered at run-time.

Fetching into a custom class

Queries can be fetched into objects based on custom classes. For example, if we have a class named ExampleClass the following query will

Dynamic queries

Dynamic queries in Drupal 7 Database API.

• Introduction to dynamic queries
• Conditional clauses
• Count queries
• Distinct
• Expressions
• Extenders
• Fields
• Grouping
• Joins
• Ordering
• Query alteration (tagging)
• Ranges and limits
• Table sorting
• Unions

Result sets

A Select query will always return a result set object of zero or more records. There are several ways to then retrieve data from that

Insert queries

Insert queries must always use a query builder object. Certain databases require special handling for LOB (Large OBject, such as TEXT in

Update queries

Update queries must always use a query builder object. Certain databases require special handling for LOB (Large OBject, such as TEXT on

Delete queries

Delete queries must always use a query builder object. They are started using the db_delete() function as follows:

Merge queries using db_merge

Merge queries are a special type of hybrid query. Although a syntax is defined for them in the SQL 2003 specification, virtually no

Writing database drivers

Coming soon, really! webchick insisted I post the documentation as it stands now, and this part isn't done yet. I'll get it added just as

Error handling

The Database API throws exceptions on error, which can be picked up by wrapping your database operations in try {} catch() {} blocks, as

Transactions

Drupal also supports transactions, including a transparent fallback for databases that do not support transactions. However, transactions

Chaining

There is a lot of talk about chaining database api functions together, for example:

Functions and operators

Drupal's database layer does not provide cross-database abstraction of SQL functions. For portability across supported database engines

SQL Views

The theory behind SQL Views, and the difference with the Views module.