[Sommaire] [Imprimer]

   1  
   2  
   3  Creole ODBC Bridge Driver
   4  =========================
   5  
   6  
   7  I. Overview
   8  -----------
   9  
  10  In the text below, the word "driver" can get somewhat muddled since there are 
  11  two libraries concerned here (Creole & ODBC). So, we'll use the term "bridge 
  12  driver" to refer to Creole's ODBC bridge driver, and "ODBC driver" to refer to 
  13  an ODBC database driver.
  14  
  15  The Creole ODBC Bridge driver provides a solution for databases which 
  16  currently have no PHP-native interface. It is currently in an experimental
  17  stage of development. It has been tested with two ODBC drivers (Sequiter's
  18  CodeBase ODBC driver and the MySQL ODBC driver (as a baseline test)). To
  19  use any other ODBC drivers you may need to write your own ODBCAdapter-derived
  20  class (see below).
  21  
  22  
  23  II. ODBCAdapter
  24  ---------------
  25  
  26  Because ODBC itself is a database abstraction library, the bridge driver needed
  27  a way of hiding ODBC driver-specific behavior. The solution to this was to 
  28  create an adapter layer (akin to how the Propel runtime engine works). Think of
  29  it as a sub-driver for the bridge driver. Any ODBC driver-specific behavior is
  30  handled by an ODBCAdapter-derived class. To use a specific adapter class, you
  31  specify its name via a parameter in the connection string:
  32  
  33  odbc://localhost/DSN=CodeBase;?adapter=CodeBase
  34  
  35  The string above will load the following file as the adapter to use with the
  36  bridge driver: creole/drivers/odbc/adapters/CodeBaseAdapter.php
  37  
  38  Some ODBC drivers are limited in support for various Creole features. The 
  39  ODBCAdapter also provides a method for emulation of some of these missing 
  40  features:
  41  
  42      -The emulatePrepareStmt() method provides a switch for enabling prepared
  43       statement emulation for drivers that do not support (or have trouble with)
  44       prepared statements. This emulation is disabled by default.
  45       
  46      -The hasLimitOffset() method provides a switch for enabling LIMIT/OFFSET 
  47       emulation for drivers that do not support this. This emulation is enabled
  48       by default. The LIMIT/OFFSET emulation was borrowed from the MSSQL Creole 
  49       driver.
  50  
  51      -The createResultSet() method provides a switch for enabling cached 
  52       result sets. To enable this feature, return an instance of 
  53       ODBCCachedResultSet in the createResultSet() method of your ODBCAdapter-
  54       derived class. This can be useful as a workaround for ODBC drivers which
  55       lack support for record count retrieval, reverse/absolute cursor
  56       scrolling, etc. In most cases, result rows are cached on-demand. So if 
  57       you only read the first couple rows of a result, then only those rows will 
  58       be cached.
  59  
  60      -The getIdGenerator() method provides a switch for enabling sequence
  61       emulation. This feature is enabled by default in ODBCAdapter and is 
  62       implemented in the ODBCIdGenerator class. The emulation code was inspired
  63       by the PEAR::DB nextID() method. If your database supports sequences or
  64       autoincrement natively, you can return your own IdGenerator-derived class 
  65       instead. Check out some of the other Creole drivers for IdGenerator 
  66       examples.
  67       
  68       
  69  III. Incomplete Features
  70  ------------------------
  71  
  72      -The database metadata classes are not fully tested/complete. Specifically, 
  73       the ODBCDatabaseInfo class does not currently set the database name. There 
  74       may be other problems as well. 
  75   
  76      -The Creole CallableStatement class (stored procedures) is not currently 
  77       implemented. No immediate plans to do this in the future, but it looks
  78       feasible.
  79  
  80  
  81  IV. Known Issues
  82  ----------------
  83  
  84  This driver was developed using the PHP v5.0 final build. During the course 
  85  of testing I uncovered several bugs in the php_odbc module. I submitted
  86  patches for these bugs, but have not yet received word that they were 
  87  committed (they were just submitted this morning). If you want more details
  88  on the problems I encountered or would like a copy of the patches, please
  89  e-mail me (dlawson@masterytech.com).
  90