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POCan nhibernate check for unique constraints, without it being the primary key
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  1. POCan nhibernate check for unique constraints, without it being the primary key
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    copied!<p>I have a simple class, that has a <code>Name</code> member, used to uniquely identify an instance. This class is referenced in a ManyToMany-mapping which will use the <code>Name</code>(since it is the primary key) to create the mapping-table. The type of strings involved makes this very slow (length > 128 chars, often only differing in the last few). To speed it up I'd like to create an <code>auto_increment</code> column (I'm using MySQL) for the join, while still being able to have nhibernate sort out the uniqueness of my objects using the <code>Name</code>-column.</p> <p>Here is an example of what it looks like. In reality the objects are a lot larger.</p> <pre><code>class MyObject{ public String Name; public String Value; } //Mapping Id(x =&gt; x.Name) .Length(255) .Unique(); Map(x =&gt; x.Value); </code></pre> <p>This works as intended. If I add a new <code>MyObject</code> to the table nhibernate will do a select first to see if a record with the same <code>Name</code> is already in the table.</p> <p>I have an <code>ObjectHolder</code> that has a Set of <code>MyObject</code></p> <pre><code>class ObjectHolder{ public UInt64 Id; public ICollection&lt;MyObject&gt; MyObjects; } //Mapping Id(x =&gt; x.Id) .GeneratedBy.Native(); HasManyToMany(x =&gt; x.MyObjects) .AsSet() .Cascade.SaveUpdate(); </code></pre> <p>This will create a mapping using <code>ObjectHolder.Id</code> and <code>MyObject.Name</code>, which is slow. I want the <code>MyObject</code> to have an Id-column that is autogenerated and only used for the mapping-table, but not for the select-to-see-if-it-exists-checking that nhibernate does with the primary key.</p> <p>I have altered the mapping to</p> <pre><code>class MyObject{ public UInt64 Id; public String Name; public String Value; } //Mapping Id(x =&gt; x.Id) .GeneratedBy.Native(); Map(x =&gt; x.Name) .Length(255) .Unique(); Map(x =&gt; x.Value); </code></pre> <p>This will create an auto_increment column and use it for the mapping-table, however it will now no longer check correctly if a record with the same <code>Name</code> already exists, which leads to duplicate entry exceptions.</p> <p>Can I tell nhibernate to check the <code>Name</code> column instead the id, or annotate the <code>Id</code>-column so it is only used as a foreign key, but nothing else? Do I have to modify the manyToMany mapping?</p> <p>Edit: It seems even worse if I have to use composite ids. All id properties are saved twice, once in the object itself and once in the mapping, which adds a huge time and storage space overhead.</p>
 

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