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<h2>java.jdbc - Using DDL and Metadata</h2>
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<h2 id="contents">Contents</h2><ul><li><a href="home.html">Overview</a></li><li><a href="using_sql.html">Using SQL</a></li><li><a href="using_ddl.html">Using DDL</a></li><li><a href="reusing_connections.html">Reusing Connections</a></li></ul><h2 id="using-ddl">Using DDL</h2><p>DDL operations can be executed using the <code>db-do-commands</code> function. The general
approach is:</p><pre><code class="clojure">(jdbc/db-do-commands db-spec [sql-command-1 sql-command-2 .. sql-command-n])
</code></pre><p>The commands are executed as a single, batched statement, wrapped in a
transaction. If you want to avoid the transaction, use this approach:</p><pre><code class="clojure">(jdbc/db-do-commands db-spec false [sql-command-1 sql-command-2 .. sql-command-n])
</code></pre><p>This is necessary for some databases that do not allow DDL operations to be
wrapped in a transaction.</p><h3 id="creating-tables">Creating tables</h3><p>For the common operations of creating and dropping tables, <code>java.jdbc</code> provides a
little assistance that recognizes <code>:entities</code> so you can use keywords (or
strings) and have your chosen naming strategy applied, just as you can for
several of the SQL functions.</p><pre><code class="clojure">(jdbc/create-table-ddl :fruit
[[:name "varchar(32)" :primary :key]
[:appearance "varchar(32)"]
[:cost :int]
[:grade :real]]
{:table-spec "ENGINE=InnoDB"
:entities clojure.string/upper-case})
</code></pre><p>This will generate:</p><pre><code class="clojure">CREATE TABLE FRUIT
(NAME varchar(32) primary key,
APPEARANCE varchar(32),
COST int,
GRADE real) ENGINE=InnoDB
</code></pre><p>which you can pass to <code>db-do-commands</code>.</p><p><code>create-table-ddl</code> also supports a <code>conditional?</code> option which can be a simple
<code>Boolean</code>, which, if <code>true</code>, will add <code>IF NOT EXISTS</code> before the table name. If
that syntax doesn't work for your database, you can pass a string that will be
used instead. If that isn't enough, you can pass a function of two arguments:
the first argument will be the table name and the second argument will be the
DDL string (this approach is needed for Microsoft SQL Server).</p><h3 id="dropping-tables">Dropping tables</h3><p>Similarly there is a <code>drop-table-ddl</code> function which takes a table name and an
optional <code>:entities</code> option to generate DDL to drop a table.</p><pre><code class="clojure">(jdbc/drop-table-ddl :fruit) ; drop table fruit
(jdbc/drop-table-ddl :fruit {:entities clojure.string/upper-case}) ; drop table FRUIT
</code></pre><p>This will generate:</p><pre><code class="clojure">DROP TABLE FRUIT
</code></pre><p><code>drop-table-ddl</code> also supports a <code>conditional?</code> option which can be a simple
<code>Boolean</code>, which, if <code>true</code>, will add <code>IF EXISTS</code> before the table name. If
that syntax doesn't work for your database, you can pass a string that will be
used instead. If that isn't enough, you can pass a function of two arguments:
the first argument will be the table name and the second argument will be the
DDL string (this approach is needed for Microsoft SQL Server).</p><h2 id="accessing-metadata">Accessing metadata</h2><p><code>java.jdbc</code> provides two functions for working with database metadata:</p><ul><li><code>with-db-metadata</code> for creating an active metadata object backed by an open
connection</li><li><code>metadata-result</code> for turning metadata results into Clojure data structures</li></ul><p>For example:</p><pre><code class="clojure">(jdbc/with-db-metadata [md db-spec]
(jdbc/metadata-result (.getTables md nil nil nil (into-array ["TABLE" "VIEW"]))))
</code></pre><p>This returns a sequence of maps describing all the tables and views in the
current database. <code>metadata-result</code> only transforms <code>ResultSet</code> objects, other
results are returned as-is. <code>metadata-result</code> can also accept an options map
containing <code>:identifiers</code> and <code>:as-arrays?</code>, like the <code>query</code> function,
and those options control how the metatadata is transformed and/or returned.</p><p>Both <code>with-db-metadata</code> and <code>metadata-result</code> can accept an options hash map
which will be passed through various <code>java.jdbc</code> functions (<code>get-connections</code>
for the former and <code>result-set-seq</code> for the latter).</p>
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