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627 lines
26 KiB
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<title>DB::QueryMethods - github.com/crystal-lang/crystal-db</title>
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<li class="parent open current" data-id="github.com/crystal-lang/crystal-db/DB" data-name="db">
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<a href="../DB.html">DB</a>
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<li class=" " data-id="github.com/crystal-lang/crystal-db/DB/Any" data-name="db::any">
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<a href="../DB/Any.html">Any</a>
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<a href="../DB/ExecResult.html">ExecResult</a>
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<li class=" " data-id="github.com/crystal-lang/crystal-db/DB/Mappable" data-name="db::mappable">
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<a href="../DB/Mappable.html">Mappable</a>
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<li class=" " data-id="github.com/crystal-lang/crystal-db/DB/MappingException" data-name="db::mappingexception">
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<a href="../DB/MappingException.html">MappingException</a>
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<li class="parent " data-id="github.com/crystal-lang/crystal-db/DB/Pool" data-name="db::pool(t)">
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<a href="../DB/Pool.html">Pool</a>
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<a href="../DB/Pool/TimeoutHelper.html">TimeoutHelper</a>
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<li class=" " data-id="github.com/crystal-lang/crystal-db/DB/PoolRetryAttemptsExceeded" data-name="db::poolretryattemptsexceeded">
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<a href="../DB/PoolRetryAttemptsExceeded.html">PoolRetryAttemptsExceeded</a>
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<a href="../DB/PoolStatement.html">PoolStatement</a>
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<li class=" " data-id="github.com/crystal-lang/crystal-db/DB/PoolTimeout" data-name="db::pooltimeout">
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<a href="../DB/PoolTimeout.html">PoolTimeout</a>
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<li class=" current" data-id="github.com/crystal-lang/crystal-db/DB/QueryMethods" data-name="db::querymethods">
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<a href="../DB/QueryMethods.html">QueryMethods</a>
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<li class=" " data-id="github.com/crystal-lang/crystal-db/DB/ResultSet" data-name="db::resultset">
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<a href="../DB/ResultSet.html">ResultSet</a>
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<li class=" " data-id="github.com/crystal-lang/crystal-db/DB/Statement" data-name="db::statement">
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<a href="../DB/Statement.html">Statement</a>
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<li class=" " data-id="github.com/crystal-lang/crystal-db/DB/StatementMethods" data-name="db::statementmethods">
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<a href="../DB/StatementMethods.html">StatementMethods</a>
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<li class=" " data-id="github.com/crystal-lang/crystal-db/DB/StringKeyCache" data-name="db::stringkeycache(t)">
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<a href="../DB/StringKeyCache.html">StringKeyCache</a>
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</ul>
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</ul>
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</div>
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<div id="main-content">
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<h1 class="type-name">
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<span class="kind">module</span> DB::QueryMethods
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</h1>
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<h2>Overview</h2>
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<p>Methods to allow querying a database.
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All methods accepts a <code>query : String</code> and a set arguments.</p>
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<p>Three kind of statements can be performed:</p>
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<ol><li><code><a href="../DB/QueryMethods.html#exec%28query%2C%2Aargs%29-instance-method">#exec</a></code> waits no record response from the database. An <code><a href="../DB/ExecResult.html">ExecResult</a></code> is returned.</li><li><code><a href="../DB/QueryMethods.html#scalar%28query%2C%2Aargs%29-instance-method">#scalar</a></code> reads a single value of the response. A union of possible values is returned.</li><li><code><a href="../DB/QueryMethods.html#query%28query%2C%2Aargs%29-instance-method">#query</a></code> returns a <code><a href="../DB/ResultSet.html">ResultSet</a></code> that allows iteration over the rows in the response and column information.</li></ol>
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<p>Arguments can be passed by position</p>
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<pre><code>db.query(<span class="s">"SELECT name FROM ... WHERE age > ?"</span>, age)</code></pre>
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<p>Convention of mapping how arguments are mapped to the query depends on each driver.</p>
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<p>Including <code><a href="../DB/QueryMethods.html">QueryMethods</a></code> requires a <code>prepare(query) : <a href="../DB/Statement.html">Statement</a></code> method that is not expected
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to be called directly.</p>
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<h2>Direct including types</h2>
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<ul class="other-types-list">
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<li class="other-type"><a href="../DB/Connection.html">DB::Connection</a></li>
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<li class="other-type"><a href="../DB/Database.html">DB::Database</a></li>
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</ul>
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<h2>Defined in:</h2>
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<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L20" target="_blank">db/query_methods.cr</a>
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<br/>
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<h2>Instance Method Summary</h2>
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<ul class="list-summary">
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<li class="entry-summary">
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<a href="#exec%28query%2C%2Aargs%29-instance-method" class="signature"><strong>#exec</strong>(query, *args)</a>
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<div class="summary"><p>Performs the <code><a href="../DB/QueryMethods.html#query%28query%2C%2Aargs%29-instance-method">#query</a></code> and returns an <code><a href="../DB/ExecResult.html">ExecResult</a></code></p></div>
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</li>
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<li class="entry-summary">
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<a href="#query%28query%2C%2Aargs%29-instance-method" class="signature"><strong>#query</strong>(query, *args)</a>
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<div class="summary"><p>Executes a <em>query</em> and returns a <code><a href="../DB/ResultSet.html">ResultSet</a></code> with the results.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query%28query%2C%2Aargs%2C%26block%29-instance-method" class="signature"><strong>#query</strong>(query, *args, &block)</a>
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<div class="summary"><p>Executes a <em>query</em> and yields a <code><a href="../DB/ResultSet.html">ResultSet</a></code> with the results.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_all%28query%2C%2Aargs%2C%26block%3AResultSet-%3EU%29%3AArray%28U%29-instance-method" class="signature"><strong>#query_all</strong>(query, *args, &block : ResultSet -> U) : Array(U)</a>
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<div class="summary"><p>Executes a <em>query</em> and yield a <code><a href="../DB/ResultSet.html">ResultSet</a></code> positioned at the beginning of each row, returning an array of the values of the blocks.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_all%28query%2C%2Aargs%2Castypes%3ATuple%29-instance-method" class="signature"><strong>#query_all</strong>(query, *args, as types : Tuple)</a>
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<div class="summary"><p>Executes a <em>query</em> and returns an array where each row is read as a tuple of the given <em>types</em>.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_all%28query%2C%2Aargs%2Castype%3AClass%29-instance-method" class="signature"><strong>#query_all</strong>(query, *args, as type : Class)</a>
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<div class="summary"><p>Executes a <em>query</em> and returns an array where there first column's value of each row is read as the given <em>type</em>.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_one%28query%2C%2Aargs%2C%26block%3AResultSet-%3EU%29%3AU-instance-method" class="signature"><strong>#query_one</strong>(query, *args, &block : ResultSet -> U) : U</a>
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<div class="summary"><p>Executes a <em>query</em> that expects a single row and yields a <code><a href="../DB/ResultSet.html">ResultSet</a></code> positioned at that first row.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_one%28query%2C%2Aargs%2Castypes%3ATuple%29-instance-method" class="signature"><strong>#query_one</strong>(query, *args, as types : Tuple)</a>
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<div class="summary"><p>Executes a <em>query</em> that expects a single row and returns it as a tuple of the given <em>types</em>.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_one%28query%2C%2Aargs%2Castype%3AClass%29-instance-method" class="signature"><strong>#query_one</strong>(query, *args, as type : Class)</a>
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<div class="summary"><p>Executes a <em>query</em> that expects a single row and returns the first column's value as the given <em>type</em>.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_one%3F%28query%2C%2Aargs%2C%26block%3AResultSet-%3EU%29%3AU%3F-instance-method" class="signature"><strong>#query_one?</strong>(query, *args, &block : ResultSet -> U) : U?</a>
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<div class="summary"><p>Executes a <em>query</em> that expects at most a single row and yields a <code><a href="../DB/ResultSet.html">ResultSet</a></code> positioned at that first row.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_one%3F%28query%2C%2Aargs%2Castypes%3ATuple%29-instance-method" class="signature"><strong>#query_one?</strong>(query, *args, as types : Tuple)</a>
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<div class="summary"><p>Executes a <em>query</em> that expects a single row and returns it as a tuple of the given <em>types</em>.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_one%3F%28query%2C%2Aargs%2Castype%3AClass%29-instance-method" class="signature"><strong>#query_one?</strong>(query, *args, as type : Class)</a>
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<div class="summary"><p>Executes a <em>query</em> that expects a single row and returns the first column's value as the given <em>type</em>.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#scalar%28query%2C%2Aargs%29-instance-method" class="signature"><strong>#scalar</strong>(query, *args)</a>
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<div class="summary"><p>Performs the <code><a href="../DB/QueryMethods.html#query%28query%2C%2Aargs%29-instance-method">#query</a></code> and returns a single scalar value puts db.scalar("SELECT MAX(name)").as(String) # => (a String)</p></div>
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</li>
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</ul>
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<div class="methods-inherited">
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</div>
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<h2>Instance Method Detail</h2>
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<div class="entry-detail" id="exec(query,*args)-instance-method">
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<div class="signature">
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def <strong>exec</strong>(query, *args)
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<a class="method-permalink" href="#exec%28query%2C%2Aargs%29-instance-method">#</a>
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</div>
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<div class="doc"><p>Performs the <code><a href="../DB/QueryMethods.html#query%28query%2C%2Aargs%29-instance-method">#query</a></code> and returns an <code><a href="../DB/ExecResult.html">ExecResult</a></code></p></div>
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<br/>
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<div>
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[<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L202" target="_blank">View source</a>]
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="entry-detail" id="query(query,*args)-instance-method">
|
||
|
|
<div class="signature">
|
||
|
|
|
||
|
|
def <strong>query</strong>(query, *args)
|
||
|
|
|
||
|
|
<a class="method-permalink" href="#query%28query%2C%2Aargs%29-instance-method">#</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="doc"><p>Executes a <em>query</em> and returns a <code><a href="../DB/ResultSet.html">ResultSet</a></code> with the results.
|
||
|
|
The <code><a href="../DB/ResultSet.html">ResultSet</a></code> must be closed manually.</p>
|
||
|
|
|
||
|
|
<pre><code>result <span class="o">=</span> db.query <span class="s">"select name from contacts where id = ?"</span>, <span class="n">10</span>
|
||
|
|
<span class="k">begin</span>
|
||
|
|
<span class="k">if</span> result.move_next
|
||
|
|
id <span class="o">=</span> result.read(<span class="t">Int32</span>)
|
||
|
|
<span class="k">end</span>
|
||
|
|
<span class="k">ensure</span>
|
||
|
|
result.close
|
||
|
|
<span class="k">end</span></code></pre></div>
|
||
|
|
|
||
|
|
<br/>
|
||
|
|
<div>
|
||
|
|
|
||
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L37" target="_blank">View source</a>]
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="entry-detail" id="query(query,*args,&block)-instance-method">
|
||
|
|
<div class="signature">
|
||
|
|
|
||
|
|
def <strong>query</strong>(query, *args, &block)
|
||
|
|
|
||
|
|
<a class="method-permalink" href="#query%28query%2C%2Aargs%2C%26block%29-instance-method">#</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="doc"><p>Executes a <em>query</em> and yields a <code><a href="../DB/ResultSet.html">ResultSet</a></code> with the results.
|
||
|
|
The <code><a href="../DB/ResultSet.html">ResultSet</a></code> is closed automatically.</p>
|
||
|
|
|
||
|
|
<pre><code>db.query(<span class="s">"select name from contacts where age > ?"</span>, <span class="n">18</span>) <span class="k">do</span> <span class="o">|</span>rs<span class="o">|</span>
|
||
|
|
rs.each <span class="k">do</span>
|
||
|
|
name <span class="o">=</span> rs.read(<span class="t">String</span>)
|
||
|
|
<span class="k">end</span>
|
||
|
|
<span class="k">end</span></code></pre></div>
|
||
|
|
|
||
|
|
<br/>
|
||
|
|
<div>
|
||
|
|
|
||
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L51" target="_blank">View source</a>]
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="entry-detail" id="query_all(query,*args,&block:ResultSet->U):Array(U)-instance-method">
|
||
|
|
<div class="signature">
|
||
|
|
|
||
|
|
def <strong>query_all</strong>(query, *args, &block : <a href="../DB/ResultSet.html">ResultSet</a> -> U) : Array(U)
|
||
|
|
|
||
|
|
<a class="method-permalink" href="#query_all%28query%2C%2Aargs%2C%26block%3AResultSet-%3EU%29%3AArray%28U%29-instance-method">#</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="doc"><p>Executes a <em>query</em> and yield a <code><a href="../DB/ResultSet.html">ResultSet</a></code> positioned at the beginning
|
||
|
|
of each row, returning an array of the values of the blocks.</p>
|
||
|
|
|
||
|
|
<pre><code>names <span class="o">=</span> db.query_all <span class="s">"select name from contacts"</span>, <span class="o">&</span>.read(<span class="t">String</span>)</code></pre></div>
|
||
|
|
|
||
|
|
<br/>
|
||
|
|
<div>
|
||
|
|
|
||
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L167" target="_blank">View source</a>]
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="entry-detail" id="query_all(query,*args,astypes:Tuple)-instance-method">
|
||
|
|
<div class="signature">
|
||
|
|
|
||
|
|
def <strong>query_all</strong>(query, *args, as types : Tuple)
|
||
|
|
|
||
|
|
<a class="method-permalink" href="#query_all%28query%2C%2Aargs%2Castypes%3ATuple%29-instance-method">#</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="doc"><p>Executes a <em>query</em> and returns an array where each row is
|
||
|
|
read as a tuple of the given <em>types</em>.</p>
|
||
|
|
|
||
|
|
<pre><code>contacts <span class="o">=</span> db.query_all <span class="s">"select name, age from contactas"</span>, <span class="k">as</span>: {<span class="t">String</span>, <span class="t">Int32</span>}</code></pre></div>
|
||
|
|
|
||
|
|
<br/>
|
||
|
|
<div>
|
||
|
|
|
||
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L183" target="_blank">View source</a>]
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="entry-detail" id="query_all(query,*args,astype:Class)-instance-method">
|
||
|
|
<div class="signature">
|
||
|
|
|
||
|
|
def <strong>query_all</strong>(query, *args, as type : Class)
|
||
|
|
|
||
|
|
<a class="method-permalink" href="#query_all%28query%2C%2Aargs%2Castype%3AClass%29-instance-method">#</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="doc"><p>Executes a <em>query</em> and returns an array where there first
|
||
|
|
column's value of each row is read as the given <em>type</em>.</p>
|
||
|
|
|
||
|
|
<pre><code>names <span class="o">=</span> db.query_all <span class="s">"select name from contactas"</span>, <span class="k">as</span>: <span class="t">String</span></code></pre></div>
|
||
|
|
|
||
|
|
<br/>
|
||
|
|
<div>
|
||
|
|
|
||
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L195" target="_blank">View source</a>]
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="entry-detail" id="query_one(query,*args,&block:ResultSet->U):U-instance-method">
|
||
|
|
<div class="signature">
|
||
|
|
|
||
|
|
def <strong>query_one</strong>(query, *args, &block : <a href="../DB/ResultSet.html">ResultSet</a> -> U) : U
|
||
|
|
|
||
|
|
<a class="method-permalink" href="#query_one%28query%2C%2Aargs%2C%26block%3AResultSet-%3EU%29%3AU-instance-method">#</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="doc"><p>Executes a <em>query</em> that expects a single row and yields a <code><a href="../DB/ResultSet.html">ResultSet</a></code>
|
||
|
|
positioned at that first row.</p>
|
||
|
|
|
||
|
|
<p>The given block must not invoke <code>move_next</code> on the yielded result set.</p>
|
||
|
|
|
||
|
|
<p>Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were no rows, or if there were more than one row.</p>
|
||
|
|
|
||
|
|
<pre><code>name <span class="o">=</span> db.query_one <span class="s">"select name from contacts where id = ?"</span>, <span class="n">18</span>, <span class="o">&</span>.read(<span class="t">String</span>)</code></pre></div>
|
||
|
|
|
||
|
|
<br/>
|
||
|
|
<div>
|
||
|
|
|
||
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L67" target="_blank">View source</a>]
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="entry-detail" id="query_one(query,*args,astypes:Tuple)-instance-method">
|
||
|
|
<div class="signature">
|
||
|
|
|
||
|
|
def <strong>query_one</strong>(query, *args, as types : Tuple)
|
||
|
|
|
||
|
|
<a class="method-permalink" href="#query_one%28query%2C%2Aargs%2Castypes%3ATuple%29-instance-method">#</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="doc"><p>Executes a <em>query</em> that expects a single row and returns it
|
||
|
|
as a tuple of the given <em>types</em>.</p>
|
||
|
|
|
||
|
|
<p>Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were no rows, or if there were more than one row.</p>
|
||
|
|
|
||
|
|
<pre><code>db.query_one <span class="s">"select name, age from contacts where id = ?"</span>, <span class="n">1</span>, <span class="k">as</span>: {<span class="t">String</span>, <span class="t">Int32</span>}</code></pre></div>
|
||
|
|
|
||
|
|
<br/>
|
||
|
|
<div>
|
||
|
|
|
||
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L85" target="_blank">View source</a>]
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="entry-detail" id="query_one(query,*args,astype:Class)-instance-method">
|
||
|
|
<div class="signature">
|
||
|
|
|
||
|
|
def <strong>query_one</strong>(query, *args, as type : Class)
|
||
|
|
|
||
|
|
<a class="method-permalink" href="#query_one%28query%2C%2Aargs%2Castype%3AClass%29-instance-method">#</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="doc"><p>Executes a <em>query</em> that expects a single row
|
||
|
|
and returns the first column's value as the given <em>type</em>.</p>
|
||
|
|
|
||
|
|
<p>Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were no rows, or if there were more than one row.</p>
|
||
|
|
|
||
|
|
<pre><code>db.query_one <span class="s">"select name from contacts where id = ?"</span>, <span class="n">1</span>, <span class="k">as</span>: <span class="t">String</span></code></pre></div>
|
||
|
|
|
||
|
|
<br/>
|
||
|
|
<div>
|
||
|
|
|
||
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L99" target="_blank">View source</a>]
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="entry-detail" id="query_one?(query,*args,&block:ResultSet->U):U?-instance-method">
|
||
|
|
<div class="signature">
|
||
|
|
|
||
|
|
def <strong>query_one?</strong>(query, *args, &block : <a href="../DB/ResultSet.html">ResultSet</a> -> U) : U?
|
||
|
|
|
||
|
|
<a class="method-permalink" href="#query_one%3F%28query%2C%2Aargs%2C%26block%3AResultSet-%3EU%29%3AU%3F-instance-method">#</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="doc"><p>Executes a <em>query</em> that expects at most a single row and yields a <code><a href="../DB/ResultSet.html">ResultSet</a></code>
|
||
|
|
positioned at that first row.</p>
|
||
|
|
|
||
|
|
<p>Returns <code>nil</code>, not invoking the block, if there were no rows.</p>
|
||
|
|
|
||
|
|
<p>Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were more than one row
|
||
|
|
(this ends up invoking the block once).</p>
|
||
|
|
|
||
|
|
<pre><code>name <span class="o">=</span> db.query_one? <span class="s">"select name from contacts where id = ?"</span>, <span class="n">18</span>, <span class="o">&</span>.read(<span class="t">String</span>)
|
||
|
|
<span class="k">typeof</span>(name) <span class="c"># => String | Nil</span></code></pre></div>
|
||
|
|
|
||
|
|
<br/>
|
||
|
|
<div>
|
||
|
|
|
||
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L117" target="_blank">View source</a>]
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="entry-detail" id="query_one?(query,*args,astypes:Tuple)-instance-method">
|
||
|
|
<div class="signature">
|
||
|
|
|
||
|
|
def <strong>query_one?</strong>(query, *args, as types : Tuple)
|
||
|
|
|
||
|
|
<a class="method-permalink" href="#query_one%3F%28query%2C%2Aargs%2Castypes%3ATuple%29-instance-method">#</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="doc"><p>Executes a <em>query</em> that expects a single row and returns it
|
||
|
|
as a tuple of the given <em>types</em>.</p>
|
||
|
|
|
||
|
|
<p>Returns <code>nil</code> if there were no rows.</p>
|
||
|
|
|
||
|
|
<p>Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were more than one row.</p>
|
||
|
|
|
||
|
|
<pre><code>result <span class="o">=</span> db.query_one? <span class="s">"select name, age from contacts where id = ?"</span>, <span class="n">1</span>, <span class="k">as</span>: {<span class="t">String</span>, <span class="t">Int32</span>}
|
||
|
|
<span class="k">typeof</span>(result) <span class="c"># => Tuple(String, Int32) | Nil</span></code></pre></div>
|
||
|
|
|
||
|
|
<br/>
|
||
|
|
<div>
|
||
|
|
|
||
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L138" target="_blank">View source</a>]
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="entry-detail" id="query_one?(query,*args,astype:Class)-instance-method">
|
||
|
|
<div class="signature">
|
||
|
|
|
||
|
|
def <strong>query_one?</strong>(query, *args, as type : Class)
|
||
|
|
|
||
|
|
<a class="method-permalink" href="#query_one%3F%28query%2C%2Aargs%2Castype%3AClass%29-instance-method">#</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="doc"><p>Executes a <em>query</em> that expects a single row
|
||
|
|
and returns the first column's value as the given <em>type</em>.</p>
|
||
|
|
|
||
|
|
<p>Returns <code>nil</code> if there were no rows.</p>
|
||
|
|
|
||
|
|
<p>Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were more than one row.</p>
|
||
|
|
|
||
|
|
<pre><code>name <span class="o">=</span> db.query_one? <span class="s">"select name from contacts where id = ?"</span>, <span class="n">1</span>, <span class="k">as</span>: <span class="t">String</span>
|
||
|
|
<span class="k">typeof</span>(name) <span class="c"># => String?</span></code></pre></div>
|
||
|
|
|
||
|
|
<br/>
|
||
|
|
<div>
|
||
|
|
|
||
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L155" target="_blank">View source</a>]
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="entry-detail" id="scalar(query,*args)-instance-method">
|
||
|
|
<div class="signature">
|
||
|
|
|
||
|
|
def <strong>scalar</strong>(query, *args)
|
||
|
|
|
||
|
|
<a class="method-permalink" href="#scalar%28query%2C%2Aargs%29-instance-method">#</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="doc"><p>Performs the <code><a href="../DB/QueryMethods.html#query%28query%2C%2Aargs%29-instance-method">#query</a></code> and returns a single scalar value
|
||
|
|
puts db.scalar("SELECT MAX(name)").as(String) # => (a String)</p></div>
|
||
|
|
|
||
|
|
<br/>
|
||
|
|
<div>
|
||
|
|
|
||
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/73108c169ec87d229c7b92d793748d9796d20802/src/db/query_methods.cr#L208" target="_blank">View source</a>]
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
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