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<h1><a name="kanchor36"></a>Types And Limitations</h1>
<p>There are limitations to the db4o indexing. Not all types can be indexed. </p>
<h2>Types Which Can Be Indexed</h2>
<p>Basically all primitive types like int, long, double<span MadCap:conditions="Primary..NET">, decimals, enums</span> etc can be indexed. Indexes on primitive types work extremely well.</p>
<p>Additionally you can index strings, which are handled by db4o like primitives. Strings can be arbitrary long, so a index on string is usually slower than a index on a primitive value. But it's still fast for straight lookups. Note also that a string index can only be used for equality comparison. Comparisons like contains, start with etc don't use the index.</p>
<p>The <span>DateTime, DateTimeOffset and Guid</span> <![CDATA[ ]]>can also be indexed without any issues.</p>
<p>You also can index any object reference except arrays and strings, which are handled like primitives. This means you can index a field which holds a reference to a object and then look up for objects which have a certain reference. </p>
<h2>Types Which Cannot Be Indexed</h2>
<p>Arrays and collections cannot be indexed. The current db4o index implementation cannot deal with those types. This also means that you cannot do fast look-ups on arrays or collections. </p>
<h2>Limitations</h2>
<p>Currently the index on strings cannot be used for advanced comparisons like contains, starts with etc. </p>
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