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    <p>If you're looking for optionally adding <code>AND xyz</code>, you could simply chain <code>Where</code> calls:</p> <pre><code>var projects = dataContext.Projects.Where(p =&gt; p.ProjectDescription.Contains(search)); if (isID) projects = projects.Where(p =&gt; p.ProjectID == projectID); </code></pre> <p>Unfortunately things are not so easy when you'd like to do an <code>OR xyz</code>. For this to work, you'll need to build a predicate expression by hand. <strong>It's not pretty.</strong> One way to do this is</p> <pre><code>Expression&lt;Func&lt;Project, bool&gt;&gt; predicate = p =&gt; p.ProjectDescription.Contains(search); if (isID) { ParameterExpression param = expr.Body.Parameters[0]; predicate = Expression.Lambda&lt;Func&lt;Project, bool&gt;&gt;( Expression.Or( expr.Body, Expression.Equal( Expression.Property(param, "ProjectID"), Expression.Constant(projectID))), param); } var projects = dataContext.Projects.Where(predicate); </code></pre> <p>Note that adding a condition to the existing predicate is a lot more work than creating the initial expression, because we need to completely rebuild the expression. (A predicate must always use a single parameter; declaring two expressions using lambda syntax will create two separate parameter expression objects, one for each predicate.) Note that the C# compiler does roughly the same behind the scenes when you use lambda syntax for the initial predicate.</p> <p>Note that this might look familiar if you're used to the criteria API for Hibernate, just a little more verbose.</p> <hr> <p>Note, however, that some LINQ implementations are pretty smart, so the following may also work:</p> <pre><code>var projects = dataContext.Projects.Where( p =&gt; p.ProjectDescription.Contains(search) || (isID &amp;&amp; p.ProjectID == projectID)); </code></pre> <p>YMMV, though, so do check the generated SQL.</p>
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    1. POUse Optional OR Clause in Linq.Table.Where()
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    1. USRuben
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    1. COYea this looks substantially more complicated than creating a new Criterion in Hibernate. I'm guessing LINQ doesn't support anything like that.
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      1. USJim Mitchener
    2. COTrue, it's very verbose. However, there might be a shortcut for your situation. I've expanded the description to mention this.
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