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<h2 id="streaming">Streaming queries</h2>
<p>
The following <a href="#findEach">findEach</a>, <a href="#findIterate">findIterate</a>,
and <a href="#findStream">findStream</a> are all streaming queries with mainly a
difference in terms of style using a closure, iterator or stream.
With these streaming queries we can process very large results without having to hold
all results in memory.
<em>findEach</em> would be the recommended style as it ensures all the resources
held by the query are closed without necessitating a try with resources block. Using
<em>findStream</em> and <em>findIterate</em> are equally fine with the note that we
need to ensure the QueryIterator and Stream are closed typically via <code>try with resources</code>.
</p>
<p>
From Ebean version 12.3.5 these streaming queries use an "adaptive persistence context".
This means that <a href="#findEach">findEach</a>, <a href="#findIterate">findIterate</a>,
and <a href="#findStream">findStream</a> will work equally as well against small query
results as <a href="findList">findList</a>. After 1000 beans are processed the queries adapt
the persistence context they use to ensure it does not hold all the beans (and run out of memory
when processing very large results).
</p>
<p>
Queries processing less than 1000 beans use a single normal persistence context. After 1000
beans the persistence context adapts such that it does not hold all the beans.
</p>
<h2 id="findEach">findEach</h2>
<p>
Execute the query processing the result one bean at a time.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="k">new</span> <span class="n">QCustomer</span><span class="o">()</span>
<span class="o">.</span><span class="na field">status</span><span class="o">.</span><span class="na">equalTo</span><span class="o">(</span><span class="n">Status</span><span class="o">.</span><span class="na">NEW</span><span class="o">)</span>
<span class="o">.</span><span class="na">order</span><span class="o">().</span><span class="na">id</span><span class="o">.</span><span class="na">asc</span><span class="o">()</span>
<span class="o">.</span><span class="na">findEach</span><span class="o">((</span><span class="n">Customer</span> <span class="n">customer</span><span class="o">)</span> <span class="o">-></span> <span class="o">{</span>
<span class="c1">// do something with customer</span>
<span class="n">System</span><span class="o">.</span><span class="na field">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="s">"-- visit "</span> <span class="o">+</span> <span class="n">customer</span><span class="o">);</span>
<span class="o">});</span>
</pre></div>
</div>
<h2 id="findEachWhile">findEachWhile</h2>
<p>
Like <em>findEach</em> but takes a predicate that allows us to stop processing
the result early.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="c1">// Returning false inside the predicate will stop the execution</span>
<span class="k">new</span> <span class="n">QCustomer</span><span class="o">()</span>
<span class="o">.</span><span class="na field">status</span><span class="o">.</span><span class="na">equalTo</span><span class="o">(</span><span class="n">Status</span><span class="o">.</span><span class="na">NEW</span><span class="o">)</span>
<span class="o">.</span><span class="na">order</span><span class="o">().</span><span class="na">id</span><span class="o">.</span><span class="na">asc</span><span class="o">()</span>
<span class="o">.</span><span class="na">findEachWhile</span><span class="o">((</span><span class="n">Customer</span> <span class="n">customer</span><span class="o">)</span> <span class="o">-></span> <span class="o">{</span>
<span class="c1">// do something with customer</span>
<span class="o">...</span>
<span class="c1">// return true to continue processing or false to stop</span>
<span class="k">return</span> <span class="o">(</span><span class="n">customer</span><span class="o">.</span><span class="na">getId</span><span class="o">()</span> <span class="o"><</span> <span class="mi">40</span><span class="o">);</span>
<span class="o">});</span>
</pre></div>
</div>
<h2 id="findEach-batch">findEach with batch consumer</h2>
<p>
Similar to <em>findEach</em> but batches the beans up so that they can
be processed in batches - for example process in batches of 100 at a time.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="k">new</span> <span class="n">QCustomer</span><span class="o">()</span>
<span class="o">.</span><span class="na field">status</span><span class="o">.</span><span class="na">equalTo</span><span class="o">(</span><span class="n">Status</span><span class="o">.</span><span class="na">NEW</span><span class="o">)</span>
<span class="o">.</span><span class="na">order</span><span class="o">().</span><span class="na">id</span><span class="o">.</span><span class="na">asc</span><span class="o">()</span>
<span class="o">.</span><span class="na">findEach</span><span class="o">(</span><span class="mi">100</span><span class="o">,</span> <span class="n">batch</span> <span class="o">-></span> <span class="o">{</span>
<span class="c1">// process the customers in batches of 100 at a time</span>
<span class="c1">// where batch is List<Customer></span>
<span class="o">...</span>
<span class="o">});</span>
</pre></div>
</div>
<h2 id="findStream">findStream</h2>
<p>
Execute the query processing the result as a stream.
Use a <code>try with resources</code> block to ensure the resources held by the stream are closed.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="k">try</span> <span class="o">(</span><span class="n">Stream</span><span class="o"><</span><span class="n">Customer</span><span class="o">></span> <span class="n">stream</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 field">status</span><span class="o">.</span><span class="na">equalTo</span><span class="o">(</span><span class="n">Status</span><span class="o">.</span><span class="na">NEW</span><span class="o">)</span>
<span class="o">.</span><span class="na">order</span><span class="o">().</span><span class="na">id</span><span class="o">.</span><span class="na">asc</span><span class="o">()</span>
<span class="o">.</span><span class="na">findStream</span><span class="o">())</span> <span class="o">{</span>
<span class="n">stream</span>
<span class="o">.</span><span class="na">filter</span><span class="o">(...)</span>
<span class="o">.</span><span class="na">map</span><span class="o">(..)</span>
<span class="o">.</span><span class="na">collect</span><span class="o">(...);</span>
<span class="o">}</span>
</pre></div>
</div>
<h2 id="findIterate">findIterate</h2>
<p>
Execute the query processing the result as a QueryIterator.
Use a <code>try with resources</code> block to ensure the resources held by the iterator are closed.
</p>
<div class="syntax java"><div class="highlight"><pre><span></span><span class="k">try</span> <span class="o">(</span><span class="n">QueryIterator</span><span class="o"><</span><span class="n">Customer</span><span class="o">></span> <span class="n">it</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 field">status</span><span class="o">.</span><span class="na">equalTo</span><span class="o">(</span><span class="n">Status</span><span class="o">.</span><span class="na">NEW</span><span class="o">)</span>
<span class="o">.</span><span class="na">order</span><span class="o">().</span><span class="na">id</span><span class="o">.</span><span class="na">asc</span><span class="o">()</span>
<span class="o">.</span><span class="na">findIterate</span><span class="o">())</span> <span class="o">{</span>
<span class="k">while</span> <span class="o">(</span><span class="n">it</span><span class="o">.</span><span class="na">hasNext</span><span class="o">())</span> <span class="o">{</span>
<span class="n">Customer</span> <span class="n">customer</span> <span class="o">=</span> <span class="n">it</span><span class="o">.</span><span class="na">next</span><span class="o">();</span>
<span class="o">...</span>
<span class="o">}</span>
<span class="o">}</span>
</pre></div>
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