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publishing docs for 0.5.0
2017-12-29 23:27:57 +00:00
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<h1 class="type-name">
<span class="kind">module</span> DB::QueryMethods
</h1>
<h2>Overview</h2>
<p>Methods to allow querying a database.
All methods accepts a <code>query : String</code> and a set arguments.</p>
<p>Three kind of statements can be performed:</p>
<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>
<p>Arguments can be passed by position</p>
<pre><code>db.query(<span class="s">&quot;SELECT name FROM ... WHERE age &gt; ?&quot;</span>, age)</code></pre>
<p>Convention of mapping how arguments are mapped to the query depends on each driver.</p>
<p>Including <code><a href="../DB/QueryMethods.html">QueryMethods</a></code> requires a <code>build(query) : <a href="../DB/Statement.html">Statement</a></code> method that is not expected
to be called directly.</p>
<h2>Direct including types</h2>
<ul class="other-types-list">
<li class="other-type"><a href="../DB/SessionMethods.html">DB::SessionMethods(Session, Stmt)</a></li>
<li class="other-type"><a href="../DB/SessionMethods/PreparedQuery.html">DB::SessionMethods::PreparedQuery(Session, Stmt)</a></li>
<li class="other-type"><a href="../DB/SessionMethods/UnpreparedQuery.html">DB::SessionMethods::UnpreparedQuery(Session, Stmt)</a></li>
</ul>
<h2>Defined in:</h2>
<a href="https://github.com/crystal-lang/crystal-db/blob/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L20" target="_blank">db/query_methods.cr</a>
<br/>
<h2>Instance Method Summary</h2>
<ul class="list-summary">
<li class="entry-summary">
<a href="#exec%28query%2C%2Aargs%29-instance-method" class="signature"><strong>#exec</strong>(query, *args)</a>
<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>
</li>
<li class="entry-summary">
<a href="#query%28query%2C%2Aargs%29-instance-method" class="signature"><strong>#query</strong>(query, *args)</a>
<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>
</li>
<li class="entry-summary">
<a href="#query%28query%2C%2Aargs%2C%26block%29-instance-method" class="signature"><strong>#query</strong>(query, *args, &block)</a>
<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>
</li>
<li class="entry-summary">
<a href="#query_all%28query%2C%2Aargs%2Castype%3AClass%29-instance-method" class="signature"><strong>#query_all</strong>(query, *args, as type : Class)</a>
<div class="summary"><p>Executes a <em>query</em> and returns an array where the value of each row is read as the given <em>type</em>.</p></div>
</li>
<li class="entry-summary">
<a href="#query_all%28query%2C%2Aargs%2Castypes%3ANamedTuple%29-instance-method" class="signature"><strong>#query_all</strong>(query, *args, as types : NamedTuple)</a>
<div class="summary"><p>Executes a <em>query</em> and returns an array where each row is read as a named tuple of the given <em>types</em> (the keys of the named tuple are not necessarily the column names).</p></div>
</li>
<li class="entry-summary">
<a href="#query_all%28query%2C%2Aargs%2C%26block%3AResultSet-%3EU%29%3AArray%28U%29forallU-instance-method" class="signature"><strong>#query_all</strong>(query, *args, &block : ResultSet -> U) : Array(U) forall U</a>
<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>
</li>
<li class="entry-summary">
<a href="#query_all%28query%2C%2Aargs%2Castypes%3ATuple%29-instance-method" class="signature"><strong>#query_all</strong>(query, *args, as types : Tuple)</a>
<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>
</li>
<li class="entry-summary">
<a href="#query_each%28query%2C%2Aargs%2C%26block%29-instance-method" class="signature"><strong>#query_each</strong>(query, *args, &block)</a>
<div class="summary"><p>Executes a <em>query</em> and yields the <code><a href="../DB/ResultSet.html">ResultSet</a></code> once per each row.</p></div>
</li>
<li class="entry-summary">
<a href="#query_one%28query%2C%2Aargs%2C%26block%3AResultSet-%3EU%29%3AUforallU-instance-method" class="signature"><strong>#query_one</strong>(query, *args, &block : ResultSet -> U) : U forall U</a>
<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>
</li>
<li class="entry-summary">
<a href="#query_one%28query%2C%2Aargs%2Castypes%3ATuple%29-instance-method" class="signature"><strong>#query_one</strong>(query, *args, as types : Tuple)</a>
<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>
</li>
<li class="entry-summary">
<a href="#query_one%28query%2C%2Aargs%2Castypes%3ANamedTuple%29-instance-method" class="signature"><strong>#query_one</strong>(query, *args, as types : NamedTuple)</a>
<div class="summary"><p>Executes a <em>query</em> that expects a single row and returns it as a named tuple of the given <em>types</em> (the keys of the named tuple are not necessarily the column names).</p></div>
</li>
<li class="entry-summary">
<a href="#query_one%28query%2C%2Aargs%2Castype%3AClass%29-instance-method" class="signature"><strong>#query_one</strong>(query, *args, as type : Class)</a>
<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>
</li>
<li class="entry-summary">
<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>
<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>
</li>
<li class="entry-summary">
<a href="#query_one%3F%28query%2C%2Aargs%2Castypes%3ANamedTuple%29-instance-method" class="signature"><strong>#query_one?</strong>(query, *args, as types : NamedTuple)</a>
<div class="summary"><p>Executes a <em>query</em> that expects a single row and returns it as a named tuple of the given <em>types</em> (the keys of the named tuple are not necessarily the column names).</p></div>
</li>
<li class="entry-summary">
<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>
<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>
</li>
<li class="entry-summary">
<a href="#query_one%3F%28query%2C%2Aargs%2C%26block%3AResultSet-%3EU%29%3AU%3FforallU-instance-method" class="signature"><strong>#query_one?</strong>(query, *args, &block : ResultSet -> U) : U? forall U</a>
<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>
</li>
<li class="entry-summary">
<a href="#scalar%28query%2C%2Aargs%29-instance-method" class="signature"><strong>#scalar</strong>(query, *args)</a>
<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>
</li>
</ul>
<div class="methods-inherited">
</div>
<h2>Instance Method Detail</h2>
<div class="entry-detail" id="exec(query,*args)-instance-method">
<div class="signature">
def <strong>exec</strong>(query, *args)
<a class="method-permalink" href="#exec%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 an <code><a href="../DB/ExecResult.html">ExecResult</a></code></p></div>
<br/>
<div>
[<a href="https://github.com/crystal-lang/crystal-db/blob/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L262" 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">&quot;select name from contacts where id = ?&quot;</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/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L37" target="_blank">View source</a>]
</div>
</div>
<div class="entry-detail" id="query(query,*args,&amp;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">&quot;select name from contacts where age &gt; ?&quot;</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/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L51" 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 the
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">&quot;select name from contacts&quot;</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/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L239" target="_blank">View source</a>]
</div>
</div>
<div class="entry-detail" id="query_all(query,*args,astypes:NamedTuple)-instance-method">
<div class="signature">
def <strong>query_all</strong>(query, *args, as types : NamedTuple)
<a class="method-permalink" href="#query_all%28query%2C%2Aargs%2Castypes%3ANamedTuple%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 named tuple of the given <em>types</em> (the keys of the named tuple
are not necessarily the column names).</p>
<pre><code>contacts <span class="o">=</span> db.query_all <span class="s">&quot;select name, age from contacts&quot;</span>, <span class="k">as</span>: {name: <span class="t">String</span>, age: <span class="t">Int32</span>}</code></pre></div>
<br/>
<div>
[<a href="https://github.com/crystal-lang/crystal-db/blob/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L227" target="_blank">View source</a>]
</div>
</div>
<div class="entry-detail" id="query_all(query,*args,&amp;block:ResultSet-&gt;U):Array(U)forallU-instance-method">
<div class="signature">
def <strong>query_all</strong>(query, *args, &block : <a href="../DB/ResultSet.html">ResultSet</a> -> U) : Array(U) forall U
<a class="method-permalink" href="#query_all%28query%2C%2Aargs%2C%26block%3AResultSet-%3EU%29%3AArray%28U%29forallU-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">&quot;select name from contacts&quot;</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/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L200" 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">&quot;select name, age from contacts&quot;</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/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L214" target="_blank">View source</a>]
</div>
</div>
<div class="entry-detail" id="query_each(query,*args,&amp;block)-instance-method">
<div class="signature">
def <strong>query_each</strong>(query, *args, &block)
<a class="method-permalink" href="#query_each%28query%2C%2Aargs%2C%26block%29-instance-method">#</a>
</div>
<div class="doc"><p>Executes a <em>query</em> and yields the <code><a href="../DB/ResultSet.html">ResultSet</a></code> once per each row.
The <code><a href="../DB/ResultSet.html">ResultSet</a></code> is closed automatically.</p>
<pre><code>db.query_each <span class="s">&quot;select name from contacts&quot;</span> <span class="k">do</span> <span class="o">|</span>rs<span class="o">|</span>
puts rs.read(<span class="t">String</span>)
<span class="k">end</span></code></pre></div>
<br/>
<div>
[<a href="https://github.com/crystal-lang/crystal-db/blob/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L253" target="_blank">View source</a>]
</div>
</div>
<div class="entry-detail" id="query_one(query,*args,&amp;block:ResultSet-&gt;U):UforallU-instance-method">
<div class="signature">
def <strong>query_one</strong>(query, *args, &block : <a href="../DB/ResultSet.html">ResultSet</a> -> U) : U forall U
<a class="method-permalink" href="#query_one%28query%2C%2Aargs%2C%26block%3AResultSet-%3EU%29%3AUforallU-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">&quot;select name from contacts where id = ?&quot;</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/be139c900c86e28b150b9808c74d2a4dd2bb913b/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">&quot;select name, age from contacts where id = ?&quot;</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/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L85" target="_blank">View source</a>]
</div>
</div>
<div class="entry-detail" id="query_one(query,*args,astypes:NamedTuple)-instance-method">
<div class="signature">
def <strong>query_one</strong>(query, *args, as types : NamedTuple)
<a class="method-permalink" href="#query_one%28query%2C%2Aargs%2Castypes%3ANamedTuple%29-instance-method">#</a>
</div>
<div class="doc"><p>Executes a <em>query</em> that expects a single row and returns it
as a named tuple of the given <em>types</em> (the keys of the named tuple
are not necessarily the column names).</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">&quot;select name, age from contacts where id = ?&quot;</span>, <span class="n">1</span>, <span class="k">as</span>: {name: <span class="t">String</span>, age: <span class="t">Int32</span>}</code></pre></div>
<br/>
<div>
[<a href="https://github.com/crystal-lang/crystal-db/blob/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L100" 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">&quot;select name from contacts where id = ?&quot;</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/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L114" 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">&quot;select name from contacts where id = ?&quot;</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"># =&gt; String?</span></code></pre></div>
<br/>
<div>
[<a href="https://github.com/crystal-lang/crystal-db/blob/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L188" target="_blank">View source</a>]
</div>
</div>
<div class="entry-detail" id="query_one?(query,*args,astypes:NamedTuple)-instance-method">
<div class="signature">
def <strong>query_one?</strong>(query, *args, as types : NamedTuple)
<a class="method-permalink" href="#query_one%3F%28query%2C%2Aargs%2Castypes%3ANamedTuple%29-instance-method">#</a>
</div>
<div class="doc"><p>Executes a <em>query</em> that expects a single row and returns it
as a named tuple of the given <em>types</em> (the keys of the named tuple
are not necessarily the column names).</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">&quot;select name, age from contacts where id = ?&quot;</span>, <span class="n">1</span>, <span class="k">as</span>: {age: <span class="t">String</span>, name: <span class="t">Int32</span>}
<span class="k">typeof</span>(result) <span class="c"># =&gt; NamedTuple(age: String, name: Int32) | Nil</span></code></pre></div>
<br/>
<div>
[<a href="https://github.com/crystal-lang/crystal-db/blob/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L171" 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">&quot;select name, age from contacts where id = ?&quot;</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"># =&gt; Tuple(String, Int32) | Nil</span></code></pre></div>
<br/>
<div>
[<a href="https://github.com/crystal-lang/crystal-db/blob/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L153" target="_blank">View source</a>]
</div>
</div>
<div class="entry-detail" id="query_one?(query,*args,&amp;block:ResultSet-&gt;U):U?forallU-instance-method">
<div class="signature">
def <strong>query_one?</strong>(query, *args, &block : <a href="../DB/ResultSet.html">ResultSet</a> -> U) : U? forall U
<a class="method-permalink" href="#query_one%3F%28query%2C%2Aargs%2C%26block%3AResultSet-%3EU%29%3AU%3FforallU-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">&quot;select name from contacts where id = ?&quot;</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"># =&gt; String | Nil</span></code></pre></div>
<br/>
<div>
[<a href="https://github.com/crystal-lang/crystal-db/blob/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L132" 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/be139c900c86e28b150b9808c74d2a4dd2bb913b/src/db/query_methods.cr#L268" target="_blank">View source</a>]
</div>
</div>
</div>
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