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Mar 19, 2018
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Document "entity join" and "entity projection" #1619

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e0f2b7b
Document "entity join" and "entity projection"
bahusoid Mar 18, 2018
8af2b5e
Minor adjustments, to be squashed.
fredericDelaporte Mar 18, 2018
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54 changes: 52 additions & 2 deletions doc/reference/modules/query_criteria.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -141,12 +141,35 @@ var cats = sess.CreateCriteria<Cat>()
.List<IDictionary>();
foreach ( IDictionary map in cats )
{
Cat cat = (Cat) map[CriteriaUtil.RootAlias];
Cat cat = (Cat) map[CriteriaSpecification.RootAlias];
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So NH-2122 has missed this one, good spot.

Cat kitten = (Cat) map["kt"];
}]]></programlisting>
<para>
Note that for retrieving just kittens you can also use an entity projection.
See <xref linkend="querycriteria-projection"/> for more information.
</para>

</sect1>


<sect1 id="querycriteria_entityjoin">
<title>Join entities without association (Entity joins or ad hoc joins)</title>
<para>
In criteria you have the ability to define a join to any entity, not just through a mapped association.
To achieve it, use <literal>CreateEntityAlias</literal> and <literal>CreateEntityCriteria</literal>. By example:
</para>

<programlisting><![CDATA[IList<Cat> uniquelyNamedCats = sess.CreateCriteria<Cat>("c")
.CreateEntityAlias(
"joinedCat",
Restrictions.And(
Restrictions.EqProperty("c.Name", "joinedCat.Name"),
Restrictions.NotEqProperty("c.Id", "joinedCat.Id")),
JoinType.LeftOuterJoin,
typeof(Cat).FullName)
.Add(Restrictions.IsNull("joinedCat.Id"))
.List();]]></programlisting>
</sect1>

<sect1 id="querycriteria-dynamicfetching">
<title>Dynamic association fetching</title>

Expand Down Expand Up @@ -286,6 +309,33 @@ var results = session.CreateCriteria<Cat>()
.AddOrder( Order.Asc("kitName") )
.List<object[]>();]]></programlisting>

<para>
You can also add an entity projection to a criteria query:
</para>

<programlisting><![CDATA[var kittens = sess.CreateCriteria<Cat>()
.CreateCriteria("Kittens", "kt")
.Add(Expression.Eq("Name", "F%"))
.SetProjection(Projections.Entity(typeof(Cat), "kt"))
.List();]]></programlisting>

<programlisting><![CDATA[var cats = sess.CreateCriteria<Cat>()
.CreateCriteria("Kittens", "kt")
.Add(Expression.Eq("Name", "F%"))
.SetProjection(
Projections.RootEntity(),
Projections.Entity(typeof(Cat), "kt"))
.List<object[]>();

foreach (var objs in cats)
{
Cat cat = (Cat) objs[0];
Cat kitten = (Cat) objs[1];
}]]></programlisting>

<para>
See <xref linkend="queryqueryover-projectionentities"/> for more information.
</para>
</sect1>

<sect1 id="querycriteria-detachedqueries">
Expand Down
45 changes: 45 additions & 0 deletions doc/reference/modules/query_queryover.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -213,6 +213,25 @@ IList<Cat> cats =

</sect1>

<sect1 id="queryqueryover_entityjoin">
<title>Join entities without association (Entity joins or ad hoc joins)</title>
<para>
In QueryOver you have the ability to define a join to any entity, not just through a mapped association.
To achieve it, use <literal>JoinEntityAlias</literal> and <literal>JoinEntityQueryOver</literal>. By example:
</para>

<programlisting><![CDATA[Cat cat = null;
Cat joinedCat = null;

var uniquelyNamedCats = sess.QueryOver<Cat>(() => cat)
.JoinEntityAlias(
() => joinedCat,
() => cat.Name == joinedCat.Name && cat.Id != joinedCat.Id,
JoinType.LeftOuterJoin)
.Where(() => joinedCat.Id == null)
.List();]]></programlisting>
</sect1>

<sect1 id="queryqueryover-aliases">
<title>Aliases</title>

Expand Down Expand Up @@ -350,6 +369,32 @@ IList<CatSummary> catReport =

</sect1>

<sect1 id="queryqueryover-projectionentities">
<title>Entities Projection</title>

<para>
You can add entity projections via the <literal>AsEntity()</literal> extension.
</para>

<programlisting><![CDATA[Cat mate = null;

var catAndMateNameList = sess.QueryOver<Cat>()
.JoinAlias(c => c.Mate, () => mate)
.Select(c => c.AsEntity(), c => mate.Name)
.List<object[]>();]]></programlisting>

<para>
Or it can be done via the <literal>Projections.RootEntity</literal> and <literal>Projections.Entity</literal> methods
if more control over loaded entities is required. For instance, entity projections can be lazy loaded
or fetched with lazy properties:
</para>
<programlisting><![CDATA[.Select(
Projections.Entity(() => alias1).SetLazy(true),
Projections.Entity(() => alias2).SetFetchLazyProperties(true),
Projections.RootEntity()
)]]></programlisting>
</sect1>

<sect1 id="queryqueryover-subqueries">
<title>Sub-queries</title>

Expand Down