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Update the <any /> mapping documentation #1809

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Jul 19, 2018
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Update the <any /> mapping documentation #1809

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24 changes: 12 additions & 12 deletions doc/reference/modules/basic_mapping.xml
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Expand Up @@ -3353,24 +3353,25 @@
example, for audit logs, user session data, etc.
</para>

<programlisting><![CDATA[<any name="AnyEntity" id-type="Int64" meta-type="Eg.Custom.Class2TablenameType">
<column name="table_name"/>
<programlisting><![CDATA[<any name="AnyEntity" id-type="long" meta-type="class">
<column name="type"/>
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This does not have to be a table name.

<column name="id"/>
</any>]]></programlisting>

<para>
The <literal>meta-type</literal> attribute allows the application to specify a custom type that maps
database column values to persistent classes that have identifier properties of the type specified by
<literal>id-type</literal>. If the meta-type returns instances of <literal>System.Type</literal>,
nothing else is required. On the other hand, if it is a basic type like <literal>String</literal> or
<literal>Char</literal>, you must specify the mapping from values to classes.
<literal>id-type</literal>. If the meta-type is <literal>class</literal>, nothing else is required.
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Support of TypeType is gone since NH 2.0, as reported in NH-1403. This has been fixed by "hijacking" the TypeType alias class for instead yielding ClassMetaType when class is used in the meta-type attribute of an any mapping (or ...-to-any).
(This can be confusing for those who know class is TypeType alias, because TypeType persists the assembly qualified type name whereas ClassMetaType persists the full-name instead (no assembly in it).)

The class full name will be persisted in the database as the type of the associated entity.
On the other hand, if it is a basic type like <literal>string</literal> or
<literal>char</literal>, you must specify the mapping from values to classes.
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This is not actually true: string and any string like types may work without meta-values. In such case they work somewhat similarly to class, but without a dedicated NHibernate MetaType. That causes issues, like those not fixed in #1803. So I have decide to keep that sentence.

If we fix this, this part would have to be updated.

</para>

<programlisting><![CDATA[<any name="being" id-type="long" meta-type="string">
<meta-value value="TBL_ANIMAL" class="Animal"/>
<meta-value value="TBL_HUMAN" class="Human"/>
<meta-value value="TBL_ALIEN" class="Alien"/>
<column name="table_name"/>
<meta-value value="ANIMAL_TYPE" class="Animal"/>
<meta-value value="HUMAN_TYPE" class="Human"/>
<meta-value value="ALIEN_TYPE" class="Alien"/>
<column name="type"/>
<column name="id"/>
</any>]]></programlisting>

Expand Down Expand Up @@ -3419,9 +3420,8 @@
</callout>
<callout arearefs="any3">
<para>
<literal>meta-type</literal> (optional - defaults to <literal>Type</literal>): a type that
maps <literal>System.Type</literal> to a single database column or, alternatively, a type
that is allowed for a discriminator mapping.
<literal>meta-type</literal> (optional - defaults to <literal>string</literal>): a type
that is allowed for a discriminator mapping, or <literal>class</literal>.
</para>
</callout>
<callout arearefs="any4">
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2 changes: 1 addition & 1 deletion doc/reference/modules/collection_mapping.xml
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Expand Up @@ -1284,7 +1284,7 @@ session.Update(category); // The relationship will be saved]]></programlist
<para>
The <literal>&lt;many-to-any&gt;</literal> and <literal>&lt;index-many-to-any&gt;</literal>
elements provide for true heterogeneous associations. These mapping elements work in the
same way as the <link linkend="mapping-types-anymapping"><literal>&lt;any&gt;</literal>
same way than the <link linkend="mapping-types-anymapping"><literal>&lt;any&gt;</literal>
element</link> - and should also be used rarely, if ever.
</para>

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