ADOdb

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[[v5:dictionary:Index]]\\
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====== The Data Dictionary ======
===== Introduction =====
The Data Dictionary provides a series of **'Meta-Functions'** that allow a portable method of managing the schema of databases, from simple querying of data attributes of columns to XML based routines to build and manage new tables. 
===== Portable Data Types =====

ADOdb provides a cross-platform method of identifying the data type of a field. These values can be used as a replacement in code that relies on the data type of field to produce a result. Each database driver contains a cross-reference table of datatypes that can accessed using the [[v5:dictionary:metatype|metaType()]] method.
==== Summary Of Standard Types ====
^ Type  ^ Represents Field Types                                                                                                                                                                    ^ When Using addColumnSql               ^ Example  ^
| C     | character fields that should be shown in a <input type="text"> tag                                                                                                                        | Add the length of the field           | C(20)    |
| C2    | Like a C field, but where possible a field that can hold multi-byte (unicode) data is created                                                                                             | Add the length of the field           | C2(20)   |
| X     | TeXt, large text or CLOB fields that should be shown in a <textarea>                                                                                                                      |                                       |          |
| X2    | Like an X field, but where possible creates a field that can hold multi-byte (unicode) data is created                                                                                    |                                       |          |
| XL    | On systems that support it, creates a large clob field (>32K). This may require additional database configuration. If the database does not support it, a standard clob field is created.  |                                       |          |
| B     | Blobs, or Binary Large Objects. Typically images.                                                                                                                                         |                                       |          |
| D     | Date (sometimes DateTime) field                                                                                                                                                           |                                       |          |
| T     | Timestamp field                                                                                                                                                                           |                                       |          |
| L     | Logical field (boolean or bit-field). Some databases emulate logicals using I2 fields                                                                                                     |                                       |          |
| I     | Integer field, This may be broken down further into I2,I4 or I8 types to represent small,medium and large integers. The largest integer data size is always represented by an I field     |                                       |          |
| N     | Numeric field. Includes autoincrement, numeric, floating point, real and integer.                                                                                                         | Add the precision and decimal digits  | N 14.4   |
| R     | Serial field. Includes serial, autoincrement integers. This works for selected databases. Some databases do not signify if a field is auto-increment                                      |                                       |          |
==== Using Data Types For Non-Portable Applications ====
There are benefits to using ADOdb data types even when writing an application that is not designed to be portable. The ''metaType()'' method can hide numerous data sub-types from a developer, when the difference in the field is not important. For example the following actual data types in the [[v5:database:microsoft_sql_server]] driver are all represented by the ADOdb type ''C'':

^Data Type^Description^
|-9|nvarchar|
|-8|nchar|
|1|char|
|12|varchar|
 
===== The Meta Functions =====
Metadata functions convert database specific table, column and index queries into a standardized cross-database format. 

| [[v5:dictionary:actualtype|actualType()]]            | Returns a string description of the actual data type linked to the [[v5:dictionary:metatype|metaType]] for the currently connected database  |
| [[v5:reference:connection:setcustomactualtype|setCustomActualType()]]     | Links a physical database type to a custom metatype |
| [[v5:dictionary:getcustomactualtypes|getCustomActualTypes()]]    | Returns a list of previously defined custom  |
| [[v5:dictionary:metacolumns|metaColumns()]]          | Returns a list of available columns and column type information for the supplied table name                                               |
| [[v5:dictionary:metacolumnnames|metaColumnNames()]]  | Returns a list of available columns for the supplied table name                                                                           |
| [[v5:dictionary:metadatabases|metaDatabases()]]      | Returns a list of available databases                                                                                                     |
| [[v5:dictionary:metaforeignkeys|metaForeignKeys()]]  | Returns a list of foreign keys for the supplied table name                                                                                |
| [[v5:dictionary:metaindexes|metaIndexes()]]          | Returns a list of indexes for the supplied table name                                                                                     |
| [[v5:dictionary:metaprimarykeys|metaPrimaryKeys()]]  | Returns a list of primary keys for the supplied table name                                                                                |
| [[v5:dictionary:metaprocedures|metaProcedures()]]    | Returns a list of procedures and functions for the connected database                                                                     |
| [[v5:dictionary:metatables|metaTables()]]            | Returns list of available tables for the supplied database name                                                                           |
| [[v5:dictionary:metatransaction|metaTransaction()]]  | Returns a database specific transaction mode for a provided meta transaction type                                                         |
| [[v5:dictionary:metatype|metaType()]]                | Converts database-specific data type into a portable type                                                                                 |
| [[v5:dictionary:setcustommetatype|setCustomMetaType()]] | Creates a custom, database-specific data type and defines how it is handled by inserts and updates                                                                            |
| [[v5:dictionary:getcustommetatypes|getCustomMetaTypes()]] | Returns a list of custom metatypes                                                                             |
| [[v5:reference:connection:serverinfo|serverInfo()]]            | Returns a set of server information                                                                                                       |
===== Schema Management =====
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The user id used when establishing a database connection may need specific privileges beyond normal INSERT, DELETE, UPDATE, SELECT in order to manage a schema in a database. Those privileges vary from one DBMS to another.
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==== Executing prepared code to update the schema ====

Each of the methods below returns an array of data, which should be executed using the [[v5:dictionary:executesqlarray|executeSqlArray()]] method. 

==== Creating A Database ====
| [[v5:dictionary:createdatabase|createDatabase()]]  | Returns the SQL necessary to create a database  |

==== Managing Tables ====


| [[v5:dictionary:createtablesql|createTableSql()]]  | Returns an SQL statement necessary to create a new table in the database  |
| [[v5:dictionary:changetablesql|changeTableSql()]]  | Returns an SQL statement necessary to change a table in the database      |
| [[v5:dictionary:renametablesql|renameTableSql()]]  | Returns an SQL statement necessary to rename a table in the database      |
| [[v5:dictionary:droptablesql|dropTableSql()]]      | Returns an SQL statement necessary to drop a table from the database      |

==== Managing Columns ====
| [[v5:dictionary:addcolumnsql|addColumnSql()]]        | Returns an SQL statement necessary to add a new column to an existing table in the database                   |
| [[v5:dictionary:altercolumnsql|altercolumnSql()]]    | Returns an SQL statement necessary to modify the attributes of an existing column in a table in the database  |
| [[v5:dictionary:renamecolumnsql|renameColumnSql()]]  | Returns an SQL statement necessary to rename an existing column in an existing table in the database          |
| [[v5:dictionary:dropcolumnsql|dropColumnSql()]]      | Returns an SQL statement necessary to drop an existing column from an existing table in the database          |
==== Managing Indexes ====
| [[v5:dictionary:createindexsql|createIndexSql()]]  | Returns an SQL statement necessary to add an index to an existing table in the database    |
| [[v5:dictionary:dropindexsql|dropIndexSql()]]   | Returns an SQL statement necessary to drop an existing index from a table in the database  |
==== Managing Database Column Comments ====
|[[v5:dictionary:getcommentsql]]| Returns the SQL necessary to read the comment on a column|
|[[v5:dictionary:setcommentsql]]| Returns the SQL necessary to write the comment on a column|
===== XML Driven Functions =====
See the section on [[v5:dictionary:xmlschema|ADOdb-xmlschema]] on how to extend data dictionary functions using XML