These functions build the foundation for accessing
Berkeley DB style databases.
This is a general abstraction layer for several
file-based databases. As such, functionality is limited
to a common subset of features supported by modern
databases such as Sleepycat Software's DB2. (This is
not to be confused with IBM's DB2 software, which is
supported through the ODBC
functions.)
The behaviour of various aspects depends on the
implementation of the underlying database. Functions
such as dba_optimize() and
dba_sync() will do what they promise for one
database and will do nothing for others. You have to
download and install supported dba-Handlers.
表格 1. List of DBA handlers
When invoking the
dba_open() or
dba_popen() functions, one of the handler names
must be supplied as an argument. The actually available
list of handlers is displayed by invoking
phpinfo() or
dba_handlers().
By using the
--enable-dba=shared configuration option you can
build a dynamic loadable modul to enable PHP for basic
support of dbm-style databases. You also have to add
support for at least one of the following handlers by
specifying the --with-XXXX
configure switch to your PHP configure line.
表格 2. Supported DBA handlers
To enable support for db2 add --with-db2[=DIR].
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To enable support for db3 add --with-db3[=DIR].
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To enable support for db4 add --with-db4[=DIR].
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To enable support for cdb add --with-cdb[=DIR].
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To enable support for flatfile add --with-flatfile.
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注: Up to PHP 4.3.0 you are able to add both db2 and db3 handler but only one of them can be used internally. That means that you cannot have both file formats. Starting with PHP 5.0.0 there is a configuration check avoid such missconfigurations.
The functions dba_open() and
dba_popen() return a handle to the specified
database file to access which is used by all other
dba-function calls.
DBA is binary safe and does not have any arbitrary
limits. However, it inherits all limits set by the
underlying database implementation.
All file-based databases must provide a way of
setting the file mode of a new created database, if
that is possible at all. The file mode is commonly
passed as the fourth argument to
dba_open() or
dba_popen().
You can access all entries of a database in a
linear way by using the
dba_firstkey() and
dba_nextkey() functions. You may not change the
database while traversing it.