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<h2 id="select">Select</h2>
<p>
<code>select</code> allows us to control the properties that are fetched at the root level
of the graph. We can specify to only select some properties to fetch. The result are beans
that are partially populated.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="c1">// "alias" bean that can be used in select and fetch clauses</span>
<span class="n">QCustomer</span> <span class="n">cust</span> <span class="o">=</span> <span class="n">QCustomer</span><span class="o">.</span><span class="na">alias</span><span class="o">();</span>
<span class="n">List</span><span class="o"><</span><span class="n">Customer</span><span class="o">></span> <span class="n">customers</span> <span class="o">=</span>
<span class="k">new</span> <span class="n">QCustomer</span><span class="o">()</span>
<span class="c1">// only fetch some properties of customer (partial objects)</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="n">cust</span><span class="o">.</span><span class="na">name</span><span class="o">,</span> <span class="n">cust</span><span class="o">.</span><span class="na">version</span><span class="o">,</span> <span class="n">cust</span><span class="o">.</span><span class="na">whenCreated</span><span class="o">)</span>
<span class="o">.</span><span class="na field">name</span><span class="o">.</span><span class="na">istartsWith</span><span class="o">(</span><span class="s">"Rob"</span><span class="o">)</span>
<span class="o">.</span><span class="na">findList</span><span class="o">();</span>
</pre></div>
</div>
<p>
With the above we specify the properties we want to fetch. We still get Customer entity beans returned
but they are <b>partially populated</b>.
</p>
<p>
The SQL generated by the above query has:
</p>
<div class="syntax sql"><div class="highlight"><pre><span></span><span class="k">select</span> <span class="n">t0</span><span class="p">.</span><span class="n">id</span><span class="p">,</span> <span class="n">t0</span><span class="p">.</span><span class="n">name</span><span class="p">,</span> <span class="n">t0</span><span class="p">.</span><span class="n">registered</span><span class="p">,</span> <span class="n">t0</span><span class="p">.</span><span class="k">version</span> <span class="k">from</span> <span class="n">customer</span> <span class="n">t0</span>
</pre></div>
</div>
<p>
Note that the <code>@Id</code> property is automatically included for most queries and it is
automatically exludeded for <b>distinct</b>, <b>findSingleAttribute</b> and <b>aggregation</b> queries.
</p>
<p>
Using query beans to define the select properties provides a type safe way to define what part of the
object graph to fetch.
</p>
<p>
The same query written using the query expression API is:
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="n">List</span><span class="o"><</span><span class="n">Customer</span><span class="o">></span> <span class="n">customers</span> <span class="o">=</span>
<span class="n">database</span><span class="o">.</span><span class="na">find</span><span class="o">(</span><span class="n">Customer</span><span class="o">.</span><span class="na">class</span><span class="o">)</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="s">"name, registered, version"</span><span class="o">)</span>
<span class="o">.</span><span class="na">findList</span><span class="o">();</span>
</pre></div>
</div>
<h2 id="alias" class="art">alias() - specify properties</h2>
<p>
Each query bean has a static <code>alias()</code> method that returns a query
bean that we use to specify properties for fetch in <code>select()</code> and
<code>fetch()</code>.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="c1">// customer "alias"</span>
<span class="n">QCustomer</span> <span class="n">cust</span> <span class="o">=</span> <span class="n">QCustomer</span><span class="o">.</span><span class="na">alias</span><span class="o">();</span>
<span class="c1">// contact "alias"</span>
<span class="n">QCustomer</span> <span class="n">con</span> <span class="o">=</span> <span class="n">QContact</span><span class="o">.</span><span class="na">alias</span><span class="o">();</span>
<span class="n">List</span><span class="o"><</span><span class="n">Customer</span><span class="o">></span> <span class="n">customers</span> <span class="o">=</span>
<span class="k">new</span> <span class="n">QCustomer</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="n">cust</span><span class="o">.</span><span class="na">name</span><span class="o">,</span> <span class="n">cust</span><span class="o">.</span><span class="na">version</span><span class="o">,</span> <span class="n">cust</span><span class="o">.</span><span class="na">whenCreated</span><span class="o">)</span>
<span class="o">.</span><span class="na field">contacts</span><span class="o">.</span><span class="na">fetch</span><span class="o">(</span><span class="n">con</span><span class="o">.</span><span class="na">firstName</span><span class="o">,</span> <span class="n">con</span><span class="o">.</span><span class="na">LastName</span><span class="o">,</span> <span class="n">con</span><span class="o">.</span><span class="na">email</span><span class="o">)</span>
<span class="o">.</span><span class="na field">name</span><span class="o">.</span><span class="na">istartsWith</span><span class="o">(</span><span class="s">"Rob"</span><span class="o">)</span>
<span class="o">.</span><span class="na">findList</span><span class="o">();</span>
</pre></div>
</div>
<p>
In the above we have alias beans for customer and contact. We use those to specify
which specific properties we want to fetch.
</p>
<p>
Note that we can assign <code>alias()</code> to a static final field.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">QCustomer</span> <span class="n">CUST</span> <span class="o">=</span> <span class="n">QCustomer</span><span class="o">.</span><span class="na">alias</span><span class="o">();</span>
<span class="o">...</span>
<span class="n">List</span><span class="o"><</span><span class="n">Customer</span><span class="o">></span> <span class="n">customers</span> <span class="o">=</span>
<span class="k">new</span> <span class="n">QCustomer</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="n">CUST</span><span class="o">.</span><span class="na">name</span><span class="o">)</span>
<span class="o">.</span><span class="na field">name</span><span class="o">.</span><span class="na">istartsWith</span><span class="o">(</span><span class="s">"Rob"</span><span class="o">)</span>
<span class="o">.</span><span class="na">findList</span><span class="o">();</span>
</pre></div>
</div>
<h2 id="aliasField" class="art">Alias for static imports</h2>
<p>
As an alternative to the <code>alias()</code> method each query bean also provides
a static <code>Alias</code> class for the case where we rather use static imports.
</p>
<p>
For example, we can use <em>QCustomer.Alias</em> to specify properties of customer like the below:
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="n">List</span><span class="o"><</span><span class="n">Customer</span><span class="o">></span> <span class="n">customers</span> <span class="o">=</span>
<span class="k">new</span> <span class="n">QCustomer</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="n">QCustomer</span><span class="o">.</span><span class="na field">Alias</span><span class="o">.</span><span class="na">name</span><span class="o">,</span> <span class="n">QCustomer</span><span class="o">.</span><span class="na field">Alias</span><span class="o">.</span><span class="na">whenCreated</span><span class="o">)</span>
<span class="o">.</span><span class="na">findList</span><span class="o">();</span>
</pre></div>
</div>
<p>
We can then change these to use static imports to get:
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="kn">import static</span> <span class="nn">org.domain.query.QCustomer.Alias.name</span><span class="o">;</span>
<span class="kn">import static</span> <span class="nn">org.domain.query.QCustomer.Alias.whenCreated</span><span class="o">;</span>
<span class="o">...</span>
<span class="n">List</span><span class="o"><</span><span class="n">Customer</span><span class="o">></span> <span class="n">customers</span> <span class="o">=</span>
<span class="k">new</span> <span class="n">QCustomer</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="n">name</span><span class="o">,</span> <span class="n">whenCreated</span><span class="o">)</span> <span class="c1">// using static imports of QCustomer.Alias</span>
<span class="o">.</span><span class="na">findList</span><span class="o">();</span>
</pre></div>
</div>
<p>
The limitation of using Alias like this is that if we do this for multiple query
bean types (like QCustomer.Alias and QContact.Alias) then we might get a name
clash. For example, if both had a property called whenCreated we can only static import
one of them.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="kn">import static</span> <span class="nn">...query.QCustomer.Alias.name</span><span class="o">;</span>
<span class="kn">import static</span> <span class="nn">...query.QCustomer.Alias.version</span><span class="o">;</span>
<span class="kn">import static</span> <span class="nn">...query.QCustomer.Alias.whenCreated</span><span class="o">;</span>
<span class="kn">import static</span> <span class="nn">...query.QContact.Alias.firstName</span><span class="o">;</span>
<span class="kn">import static</span> <span class="nn">...query.QContact.Alias.lastName</span><span class="o">;</span>
<span class="c1">// Use explicit QContact.Alias.whenCreated (as clash with QCustomer.Alias.whenCreated)</span>
<span class="n">List</span><span class="o"><</span><span class="n">Customer</span><span class="o">></span> <span class="n">customers</span> <span class="o">=</span>
<span class="k">new</span> <span class="n">QCustomer</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="n">name</span><span class="o">,</span> <span class="n">version</span><span class="o">,</span> <span class="n">whenCreated</span><span class="o">)</span>
<span class="o">.</span><span class="na field">contacts</span><span class="o">.</span><span class="na">fetch</span><span class="o">(</span><span class="n">firstName</span><span class="o">,</span> <span class="n">lastName</span><span class="o">,</span> <span class="n">QContact</span><span class="o">.</span><span class="na field">Alias</span><span class="o">.</span><span class="na">whenCreated</span><span class="o">)</span>
<span class="o">.</span><span class="na field">name</span><span class="o">.</span><span class="na">istartsWith</span><span class="o">(</span><span class="s">"Rob"</span><span class="o">)</span>
<span class="o">.</span><span class="na">findList</span><span class="o">();</span>
</pre></div>
</div>
<h2 id="formula" cqlass="art">Formula</h2>
<p>
We need to use this string select clause when we want to specify a formula.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="c1">// java</span>
<span class="n">List</span><span class="o"><</span><span class="n">String</span><span class="o">></span> <span class="n">names</span> <span class="o">=</span>
<span class="k">new</span> <span class="n">QContact</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="s">"concat(lastName,', ',firstName)"</span><span class="o">)</span>
<span class="o">.</span><span class="na field">lastName</span><span class="o">.</span><span class="na">startsWith</span><span class="o">(</span><span class="s">"A"</span><span class="o">)</span>
<span class="o">.</span><span class="na">findSingleAttributeList</span><span class="o">();</span>
</pre></div>
</div>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="c1">// kotlin</span>
<span class="k">var</span> <span class="n">names</span><span class="o">:</span> <span class="n">List</span><span class="o"><</span><span class="n">String</span><span class="o">></span> <span class="o">=</span>
<span class="n">QContact</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="s">"concat(lastName,' ',firstName)"</span><span class="o">)</span>
<span class="o">.</span><span class="na field">lastName</span><span class="o">.</span><span class="na">startsWith</span><span class="o">(</span><span class="s">"A"</span><span class="o">)</span>
<span class="o">.</span><span class="na">findSingleAttributeList</span><span class="o">()</span>
</pre></div>
</div>
<h5>Example - Postgis ST_Distance formula</h5>
<p>
With this example we explicitly cast to a Java BigDecimal type using
the <code>::BigDecimal</code> cast at the end of the formula.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="c1">// given route is a Postgis geometry(linestring,4326)</span>
<span class="c1">// return the distance between the start and end points</span>
<span class="n">BigDecimal</span> <span class="n">routeDistance</span> <span class="o">=</span> <span class="n">query</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="s">"ST_Distance(ST_StartPoint(route), ST_EndPoint(route))::BigDecimal"</span><span class="o">)</span>
<span class="o">.</span><span class="na">where</span><span class="o">()</span>
<span class="o">.</span><span class="na">idEq</span><span class="o">(</span><span class="n">tripId</span><span class="o">)</span>
<span class="o">.</span><span class="na">findSingleAttribute</span><span class="o">();</span>
</pre></div>
</div>
<h2 id="asDto" class="art">asDto</h2>
<p>
When we use a select formula we sometimes want to return the result into a plain <code>DTO bean</code>
rather than an entity bean. We do this using <code>.asDto(Class<D>)</code> to turn the ORM query
into a DtoQuery.
</p>
<p>
For more details refer to <a href="/docs/query/dtoquery">DTO queries</a>.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="c1">// ContactDto is a plain bean with email and fullName properties</span>
<span class="n">List</span><span class="o"><</span><span class="n">ContactDto</span><span class="o">></span> <span class="n">contacts</span> <span class="o">=</span>
<span class="k">new</span> <span class="n">QContact</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="s">"email, concat(lastName, ', ', firstName) as fullName"</span><span class="o">)</span>
<span class="o">.</span><span class="na field">lastName</span><span class="o">.</span><span class="na">startsWith</span><span class="o">(</span><span class="s">"A"</span><span class="o">)</span>
<span class="o">.</span><span class="na">orderBy</span><span class="o">()</span>
<span class="o">.</span><span class="na field">lastName</span><span class="o">.</span><span class="na">asc</span><span class="o">()</span>
<span class="o">.</span><span class="na">setMaxRows</span><span class="o">(</span><span class="mi">10</span><span class="o">)</span>
<span class="o">.</span><span class="na">asDto</span><span class="o">(</span><span class="n">ContactDto</span><span class="o">.</span><span class="na">class</span><span class="o">)</span>
<span class="o">.</span><span class="na">findList</span><span class="o">();</span>
</pre></div>
</div>
<h2 id="aggregation" class="art">Aggregation</h2>
<p>
Similar to formula queries we can use the standard aggregations of
<code>SUM, MAX, MIN, AVG and COUNT</code> in the select clause.
</p>
<p>
For more details refer to <a href="/docs/query/aggregation">Aggregation queries</a>.
</p>
<h5>Single aggregation queries</h5>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="c1">// java</span>
<span class="n">Timestamp</span> <span class="n">maxWhen</span> <span class="o">=</span>
<span class="k">new</span> <span class="n">QContact</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="s">"max(whenModified)"</span><span class="o">)</span>
<span class="o">.</span><span class="na">findSingleAttribute</span><span class="o">()</span>
</pre></div>
</div>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="c1">// kotlin</span>
<span class="k">var</span> <span class="n">maxWhen</span><span class="o">:</span> <span class="n">Timestamp</span> <span class="o">=</span>
<span class="n">QContact</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="s">"max(whenModified)"</span><span class="o">)</span>
<span class="o">.</span><span class="na">findSingleAttribute</span><span class="o">()</span>
</pre></div>
</div>
<div class="syntax sql"><div class="highlight"><pre><span></span><span class="k">select</span> <span class="k">max</span><span class="p">(</span><span class="n">t0</span><span class="p">.</span><span class="n">when_modified</span><span class="p">)</span> <span class="k">from</span> <span class="n">contact</span> <span class="n">t0</span>
</pre></div>
</div>
<h5>Group by aggregation queries</h5>
<p>
When multiple column aggregation query we use the string select clause.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="n">List</span><span class="o"><</span><span class="n">MachineStats</span><span class="o">></span> <span class="n">result</span> <span class="o">=</span>
<span class="k">new</span> <span class="n">QMachineStats</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="s">"machine, date, max(rate)"</span><span class="o">)</span>
<span class="o">.</span><span class="na field">date</span><span class="o">.</span><span class="na">gt</span><span class="o">(</span><span class="n">LocalDate</span><span class="o">.</span><span class="na">now</span><span class="o">().</span><span class="na">minusDays</span><span class="o">(</span><span class="mi">10</span><span class="o">))</span>
<span class="o">.</span><span class="na">query</span><span class="o">().</span><span class="na">having</span><span class="o">().</span><span class="na">gt</span><span class="o">(</span><span class="s">"max(rate)"</span><span class="o">,</span> <span class="mi">4</span><span class="o">)</span>
<span class="o">.</span><span class="na">findList</span><span class="o">();</span>
</pre></div>
</div>
<p>
The above query produces the following sql:
</p>
<div class="syntax sql"><div class="highlight"><pre><span></span><span class="k">select</span> <span class="n">t0</span><span class="p">.</span><span class="n">machine_id</span><span class="p">,</span> <span class="n">t0</span><span class="p">.</span><span class="nb">date</span><span class="p">,</span> <span class="k">max</span><span class="p">(</span><span class="n">t0</span><span class="p">.</span><span class="n">rate</span><span class="p">)</span>
<span class="k">from</span> <span class="n">d_machine_stats</span> <span class="n">t0</span>
<span class="k">where</span> <span class="n">t0</span><span class="p">.</span><span class="nb">date</span> <span class="o">></span> <span class="o">?</span>
<span class="k">group</span> <span class="k">by</span> <span class="n">t0</span><span class="p">.</span><span class="n">machine_id</span><span class="p">,</span> <span class="n">t0</span><span class="p">.</span><span class="nb">date</span>
<span class="k">having</span> <span class="k">max</span><span class="p">(</span><span class="n">t0</span><span class="p">.</span><span class="n">rate</span><span class="p">)</span> <span class="o">></span> <span class="o">?</span>
</pre></div>
</div>
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