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<h2>Aggregation</h2>
<p>
SQL has the aggregation functions of <code>SUM</code>, <code>MIN</code>, <code>MAX</code>, <code>COUNT</code>
and <code>AVG</code>.
</p>
<p>
We can use these functions in Ebean as <em>dynamic formula</em> or as properties
via <em>@Aggregation</em> and <em>@Sum</em>.
</p>
<p> </p>
<h2 id="dynamicformula">Dynamic formula</h2>
<h5>Single attribute</h5>
<p>
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="n">LocalDate</span> <span class="n">maxDate</span> <span class="o">=</span>
<span class="k">new</span> <span class="n">QOrder</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="s">"max(orderDate)"</span><span class="o">)</span>
<span class="o">.</span><span class="na field">customer</span><span class="o">.</span><span class="na field">name</span><span class="o">.</span><span class="na">equalTo</span><span class="o">(</span><span class="s">"Rob"</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">order_date</span><span class="p">)</span>
<span class="k">from</span> <span class="n">orders</span> <span class="n">t0</span>
<span class="k">join</span> <span class="n">customer</span> <span class="n">t1</span> <span class="k">on</span> <span class="n">t1</span><span class="p">.</span><span class="n">id</span> <span class="o">=</span> <span class="n">t0</span><span class="p">.</span><span class="n">customer_id</span>
<span class="k">where</span> <span class="n">t1</span><span class="p">.</span><span class="n">name</span> <span class="o">=</span> <span class="o">?</span> <span class="p">;</span> <span class="c1">--bind(Rob)</span>
</pre></div>
</div>
<p>
With aggregation queries that select only a single attribute the returned type
matches the property type. In the above case the orderDate is a <code>LocalDate</code>
and so that is the type returned.
</p>
<p> </p>
<h2 id="multiple">Multiple attributes</h2>
<p>
When we specify non-aggregate properties (<em>status</em> in the example below) then
a <code>GROUP BY</code> clause is generated that includes all the non-aggregate properties.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="n">List</span><span class="o"><</span><span class="n">Order</span><span class="o">></span> <span class="n">orders</span> <span class="o">=</span>
<span class="k">new</span> <span class="n">QOrder</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="s">"status, max(orderDate)"</span><span class="o">)</span> <span class="c1">// status is non-aggregate</span>
<span class="o">.</span><span class="na field">customer</span><span class="o">.</span><span class="na field">name</span><span class="o">.</span><span class="na">equalTo</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>
<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">status</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">order_date</span><span class="p">)</span>
<span class="k">from</span> <span class="n">orders</span> <span class="n">t0</span>
<span class="k">join</span> <span class="n">customer</span> <span class="n">t1</span> <span class="k">on</span> <span class="n">t1</span><span class="p">.</span><span class="n">id</span> <span class="o">=</span> <span class="n">t0</span><span class="p">.</span><span class="n">customer_id</span>
<span class="k">where</span> <span class="n">t1</span><span class="p">.</span><span class="n">name</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">status</span> <span class="c1">-- group by non-aggregate properties</span>
</pre></div>
</div>
<p>
The beans returned by aggregation queries are <em>partially populated</em>. They don't contain
the <em>@Id</em> property and thus do not support lazy loading or persisting.
</p>
<p>
The order beans in the example above will only have their <em>status</em> and <em>orderDate</em>
properties loaded.
</p>
<p> </p>
<h2 id="fetch">Fetch</h2>
<p>
Aggregation queries can include <code>fetch</code> or <code>fetchQuery</code> to load related beans.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="n">List</span><span class="o"><</span><span class="n">Order</span><span class="o">></span> <span class="n">orders</span>
<span class="o">=</span> <span class="k">new</span> <span class="n">QOrder</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="s">"status, max(orderDate)"</span><span class="o">)</span>
<span class="o">.</span><span class="na field">customer</span><span class="o">.</span><span class="na">fetch</span><span class="o">(</span><span class="s">"name"</span><span class="o">)</span> <span class="c1">// (1) fetch</span>
<span class="o">.</span><span class="na field">status</span><span class="o">.</span><span class="na">notEqualTo</span><span class="o">(</span><span class="n">Order</span><span class="o">.</span><span class="na field">Status</span><span class="o">.</span><span class="na">NEW</span><span class="o">)</span>
<span class="o">.</span><span class="na">findList</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="n">t0</span><span class="p">.</span><span class="n">status</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">order_date</span><span class="p">),</span> <span class="n">t1</span><span class="p">.</span><span class="n">id</span><span class="p">,</span> <span class="n">t1</span><span class="p">.</span><span class="n">name</span> <span class="c1">-- (1) has customer id and name</span>
<span class="k">from</span> <span class="n">orders</span> <span class="n">t0</span>
<span class="k">join</span> <span class="n">customer</span> <span class="n">t1</span> <span class="k">on</span> <span class="n">t1</span><span class="p">.</span><span class="n">id</span> <span class="o">=</span> <span class="n">t0</span><span class="p">.</span><span class="n">customer_id</span>
<span class="k">where</span> <span class="n">t0</span><span class="p">.</span><span class="n">status</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">status</span><span class="p">,</span> <span class="n">t1</span><span class="p">.</span><span class="n">id</span><span class="p">,</span> <span class="n">t1</span><span class="p">.</span><span class="n">name</span> <span class="c1">-- (1) has customer id and name</span>
</pre></div>
</div>
<p>
When we use <code>fetchQuery</code> the ORM query is executed as 2 sql queries.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="n">List</span><span class="o"><</span><span class="n">Order</span><span class="o">></span> <span class="n">orders</span>
<span class="o">=</span> <span class="k">new</span> <span class="n">QOrder</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="s">"status, max(orderDate)"</span><span class="o">)</span>
<span class="o">.</span><span class="na field">customer</span><span class="o">.</span><span class="na">fetchQuery</span><span class="o">(</span><span class="s">"name"</span><span class="o">)</span> <span class="c1">// (2) fetchQuery ...</span>
<span class="o">.</span><span class="na field">status</span><span class="o">.</span><span class="na">notEqualTo</span><span class="o">(</span><span class="n">Order</span><span class="o">.</span><span class="na field">Status</span><span class="o">.</span><span class="na">NEW</span><span class="o">)</span>
<span class="o">.</span><span class="na">findList</span><span class="o">();</span>
</pre></div>
</div>
<div class="syntax sql"><div class="highlight"><pre><span></span><span class="c1">-- Primary query</span>
<span class="k">select</span> <span class="n">t0</span><span class="p">.</span><span class="n">status</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">order_date</span><span class="p">),</span> <span class="n">t0</span><span class="p">.</span><span class="n">customer_id</span> <span class="c1">-- (2) has customer id only</span>
<span class="k">from</span> <span class="n">orders</span> <span class="n">t0</span>
<span class="k">where</span> <span class="n">t0</span><span class="p">.</span><span class="n">status</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">status</span><span class="p">,</span> <span class="n">t0</span><span class="p">.</span><span class="n">customer_id</span>
</pre></div>
</div>
<div class="syntax sql"><div class="highlight"><pre><span></span><span class="c1">-- Secondary query</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="c1">-- (2) customer id and name</span>
<span class="k">from</span> <span class="n">customer</span> <span class="n">t0</span>
<span class="k">where</span> <span class="n">t0</span><span class="p">.</span><span class="n">id</span> <span class="k">in</span> <span class="p">(</span><span class="o">?</span><span class="p">,</span> <span class="o">?</span><span class="p">,</span> <span class="o">?</span><span class="p">,</span> <span class="o">?</span><span class="p">,</span> <span class="o">?</span> <span class="p">)</span>
</pre></div>
</div>
<p>
Using <em>fetchQuery()</em> can be good when there are many properties on customer that
we want to load (as these all go into the secondary sql query rather than the primary
query and therefore are not part of the <em>GROUP BY</em>.
</p>
<p> </p>
<h2 id="atAggregation">@Aggregation</h2>
<p>
We can model aggregations with properties annotated with <code>@Aggregation</code>.
This is an alternative to using dynamic formula.
</p>
<p>
Properties with <em>@Aggregation</em> must be explicitly included in a query (they are considered Transient).
</p>
<h5>Example:</h5>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="nd">@Entity</span>
<span class="nd">@Table</span><span class="o">(</span><span class="nx">name</span> <span class="o">=</span> <span class="s">"orders"</span><span class="o">)</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Order</span> <span class="kd">extends</span> <span class="n">BaseModel</span> <span class="o">{</span>
<span class="o">...</span>
<span class="n">LocalDate</span> <span class="n">orderDate</span><span class="o">;</span>
<span class="nd">@Aggregation</span><span class="o">(</span><span class="s">"max(orderDate)"</span><span class="o">)</span> <span class="c1">// aggregation property</span>
<span class="n">LocalDate</span> <span class="n">maxOrderDate</span><span class="o">;</span>
<span class="nd">@Aggregation</span><span class="o">(</span><span class="s">"count(*)"</span><span class="o">)</span> <span class="c1">// aggregation property</span>
<span class="n">Long</span> <span class="n">totalCount</span><span class="o">;</span>
</pre></div>
</div>
<p>
Having added the <em>maxOrderDate</em> and <em>totalCount</em> properties we can use
them in <code>select</code> and <code>having</code> clauses in our queries.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="n">QOrder</span> <span class="n">o</span> <span class="o">=</span> <span class="n">QOrder</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">Order</span><span class="o">></span> <span class="n">orders</span> <span class="o">=</span> <span class="k">new</span> <span class="n">QOrder</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="n">o</span><span class="o">.</span><span class="na">status</span><span class="o">,</span> <span class="n">o</span><span class="o">.</span><span class="na">maxOrderDate</span><span class="o">,</span> <span class="n">o</span><span class="o">.</span><span class="na">totalCount</span><span class="o">)</span>
<span class="o">.</span><span class="na">findList</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="n">t0</span><span class="p">.</span><span class="n">status</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">order_date</span><span class="p">),</span> <span class="k">count</span><span class="p">(</span><span class="o">*</span><span class="p">)</span>
<span class="k">from</span> <span class="n">orders</span> <span class="n">t0</span>
<span class="k">group</span> <span class="k">by</span> <span class="n">t0</span><span class="p">.</span><span class="n">status</span>
</pre></div>
</div>
<h4>Having</h4>
<p>
Predicates on aggregation properties should be added to the <code>Having</code> clause.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="n">List</span><span class="o"><</span><span class="n">Order</span><span class="o">></span> <span class="n">orders</span> <span class="o">=</span> <span class="k">new</span> <span class="n">QOrder</span><span class="o">()</span>
<span class="o">.</span><span class="na">select</span><span class="o">(</span><span class="n">o</span><span class="o">.</span><span class="na">status</span><span class="o">,</span> <span class="n">o</span><span class="o">.</span><span class="na">maxOrderDate</span><span class="o">,</span> <span class="n">o</span><span class="o">.</span><span class="na">totalCount</span><span class="o">)</span>
<span class="o">.</span><span class="na field">status</span><span class="o">.</span><span class="na">notEqualTo</span><span class="o">(</span><span class="n">Order</span><span class="o">.</span><span class="na field">Status</span><span class="o">.</span><span class="na">COMPLETE</span><span class="o">)</span> <span class="c1">// (1) where clause - non aggregate properties</span>
<span class="o">.</span><span class="na">having</span><span class="o">()</span>
<span class="o">.</span><span class="na field">totalCount</span><span class="o">.</span><span class="na">greaterThan</span><span class="o">(</span><span class="mi">1</span><span class="o">)</span> <span class="c1">// (2) having clause - aggregate properties</span>
<span class="o">.</span><span class="na">findList</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="n">t0</span><span class="p">.</span><span class="n">status</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">order_date</span><span class="p">),</span> <span class="k">count</span><span class="p">(</span><span class="o">*</span><span class="p">)</span>
<span class="k">from</span> <span class="n">orders</span> <span class="n">t0</span>
<span class="k">where</span> <span class="n">t0</span><span class="p">.</span><span class="n">status</span> <span class="o"><></span> <span class="o">?</span> <span class="o">//</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="k">group</span> <span class="k">by</span> <span class="n">t0</span><span class="p">.</span><span class="n">status</span>
<span class="k">having</span> <span class="k">count</span><span class="p">(</span><span class="o">*</span><span class="p">)</span> <span class="o">></span> <span class="o">?</span> <span class="o">//</span> <span class="p">(</span><span class="mi">2</span><span class="p">)</span>
</pre></div>
</div>
<p> </p>
<h2 id="beans">Aggregation beans</h2>
<p>
If we only want 1 or 2 aggregation properties we feel ok adding these to the existing entity beans.
However, if instead we have many properties we want to aggregate this approach is <em>messing with
our model and it starts to look ugly.</em>
</p>
<p>
We can create <em>aggregation beans</em> to model the properties - model the sum/group by/aggregation
view.
</p>
<ul>
<li>Use @View rather than @Table</li>
<li>Does not extend Model as we don't save() or delete() these</li>
<li>Does not have @Id or @Version properties</li>
<li>Has properties we want to Aggregate on (sum, max etc)</li>
<li>Has properties we want to group by on (date, status, ManyToOne)</li>
</ul>
<h4>Example</h4>
<p>
Say we have an entity bean called <em>MachineUse</em> with:
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="nd">@Entity</span>
<span class="nd">@Table</span><span class="o">(</span><span class="nx">name</span> <span class="o">=</span> <span class="s">"machine_use"</span><span class="o">)</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">MachineUse</span> <span class="kd">extends</span> <span class="n">Model</span> <span class="o">{</span>
<span class="nd">@Id</span>
<span class="kd">private</span> <span class="kt">long</span> <span class="n">id</span><span class="o">;</span>
<span class="nd">@ManyToOne</span><span class="o">(</span><span class="nx">optional</span> <span class="o">=</span> <span class="kc">false</span><span class="o">)</span>
<span class="kd">private</span> <span class="n">DMachine</span> <span class="n">machine</span><span class="o">;</span>
<span class="kd">private</span> <span class="n">LocalDate</span> <span class="n">date</span><span class="o">;</span>
<span class="kd">private</span> <span class="kt">long</span> <span class="n">distanceKms</span><span class="o">;</span> <span class="c1">// we want to sum() this ...</span>
<span class="kd">private</span> <span class="kt">long</span> <span class="n">timeSecs</span><span class="o">;</span> <span class="c1">// we want to sum() this ...</span>
<span class="kd">private</span> <span class="n">BigDecimal</span> <span class="n">fuel</span><span class="o">;</span> <span class="c1">// we want to sum() this ...</span>
<span class="nd">@Version</span>
<span class="kd">private</span> <span class="kt">long</span> <span class="n">version</span><span class="o">;</span>
<span class="o">...</span>
</pre></div>
</div>
<p>
We can create the aggregate bean for this as:
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="nd">@Entity</span>
<span class="nd">@View</span><span class="o">(</span><span class="nx">name</span> <span class="o">=</span> <span class="s">"machine_use"</span><span class="o">)</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">MachineUseAggregate</span> <span class="o">{</span>
<span class="nd">@ManyToOne</span><span class="o">(</span><span class="nx">optional</span> <span class="o">=</span> <span class="kc">false</span><span class="o">)</span>
<span class="kd">private</span> <span class="n">DMachine</span> <span class="n">machine</span><span class="o">;</span> <span class="c1">// group by, fetch, fetchQuery on ...</span>
<span class="kd">private</span> <span class="n">LocalDate</span> <span class="n">date</span><span class="o">;</span> <span class="c1">// group by on ...</span>
<span class="nd">@Aggregation</span><span class="o">(</span><span class="s">"sum(distanceKms)"</span><span class="o">)</span>
<span class="kd">private</span> <span class="n">Long</span> <span class="n">distanceKms</span><span class="o">;</span>
<span class="nd">@Aggregation</span><span class="o">(</span><span class="s">"sum(timeSecs)"</span><span class="o">)</span>
<span class="kd">private</span> <span class="n">Long</span> <span class="n">timeSecs</span><span class="o">;</span>
<span class="nd">@Aggregation</span><span class="o">(</span><span class="s">"sum(fuel)"</span><span class="o">)</span>
<span class="kd">private</span> <span class="n">BigDecimal</span> <span class="n">fuel</span><span class="o">;</span>
<span class="nd">@Aggregation</span><span class="o">(</span><span class="s">"count(*)"</span><span class="o">)</span>
<span class="kd">private</span> <span class="n">Long</span> <span class="n">count</span><span class="o">;</span>
<span class="o">...</span>
</pre></div>
</div>
<p> </p>
<h2 id="atSum">@Sum</h2>
<p>
When we create <em>aggregation beans</em> we very often see the pattern where we sum a property like:
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="nd">@Aggregation</span><span class="o">(</span><span class="s">"sum(<property name>)"</span><span class="o">)</span>
<span class="n">Type</span> <span class="o"><</span><span class="n">property</span> <span class="n">name</span><span class="o">>;</span>
</pre></div>
</div>
<p> </p>
<p>
For example, we see beans like:
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="nd">@Aggregation</span><span class="o">(</span><span class="s">"sum(distanceKms)"</span><span class="o">)</span>
<span class="n">BigDecimal</span> <span class="n">distanceKms</span><span class="o">;</span>
<span class="nd">@Aggregation</span><span class="o">(</span><span class="s">"sum(useSeconds)"</span><span class="o">)</span>
<span class="n">Long</span> <span class="n">useSeconds</span><span class="o">;</span>
<span class="nd">@Aggregation</span><span class="o">(</span><span class="s">"sum(cost)"</span><span class="o">)</span>
<span class="n">BigDecimal</span> <span class="n">cost</span><span class="o">;</span>
</pre></div>
</div>
<p> </p>
<p>
<code>@Sum</code> is syntatic sugar for this pattern and the above becomes:
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="nd">@Sum</span>
<span class="n">BigDecimal</span> <span class="n">distanceKms</span><span class="o">;</span>
<span class="nd">@Sum</span>
<span class="n">Long</span> <span class="n">useSeconds</span><span class="o">;</span>
<span class="nd">@Sum</span>
<span class="n">BigDecimal</span> <span class="n">cost</span><span class="o">;</span>
</pre></div>
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