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<h2 class="title" style="clear: both"><a id="am_misc_db_sql"></a>Specifying a Berkeley DB schema using SQL DDL</h2>
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<p>
When starting a new Berkeley DB project, much of the code that you
must write is dedicated to defining the BDB environment: what
databases it contains, the types of the databases, and so forth.
Also, since records in BDB are just byte arrays, you must write
code that assembles and interprets these byte arrays.
</p>
<p>
Much of this code can be written automatically (in C) by the
db_sql_codegen utility. To use it, you first specify the schema of your Berkeley
DB environment in SQL Data Definition Language (DDL). Then you
invoke the db_sql_codegen command, giving the DDL as input.
<span class="command"><strong>db_sql_codegen</strong></span> reads the DDL, and writes C code that
implements a storage-layer API suggested by the DDL.
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<p>
The generated API includes a general-purpose initialization
function, which sets up the environment and the databases (creating
them if they don't already exist). It also includes C structure
declarations for each record type, and numerous specialized
functions for storing and retrieving those records.
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<span class="command"><strong>db_sql_codegen</strong></span> can also produce a simple test program
that exercises the generated API. This program is useful as an
example of how to use the API. It contains calls to all of the
interface functions, along with commentary explaining what the code
is doing.
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<p>
Once the storage layer API is produced, your application may use it
as is, or you may customize it as much as you like by editing the
generated source code. Be warned, however:
<span class="command"><strong>db_sql_codegen</strong></span> is a one-way process; there is no way to
automatically incorporate customizations into newly generated code,
if you decide to run <span class="command"><strong>db_sql_codegen</strong></span> again.
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To learn more about <span class="command"><strong>db_sql_codegen</strong></span>, please consult the
db_sql_codegen utility manual page in the Berkeley DB C API guide.
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