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POCreating a LINQ Expression where parameter equals object
 

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    <p>Given a primitive value <code>age</code> I know how to create an expression like this:</p> <pre><code>//assuming: age is an int or some other primitive type employee =&gt; employee.Age == age </code></pre> <p>By doing this:</p> <pre><code>var entityType = typeof(Employee); var propertyName = "Age"; int age = 30; var parameter = Expression.Parameter(entityType, "entity"); var lambda = Expression.Lambda( Expression.Equal( Expression.Property(parameter, propertyName), Expression.Constant(age) ) , parameter); </code></pre> <p>That works fine except in scenarios where the property and constant in question are not primitive types.</p> <p>How would I construct a similar expression if the comparison is between objects?</p> <p>With EF I can just write:</p> <pre><code>Location location = GetCurrentLocation(); employees = DataContext.Employees.Where(e =&gt; e.Location == location); </code></pre> <p><strong>That also works</strong>, but if I try to create the same expression:</p> <pre><code>var entityType = typeof(Employee); var propertyName = "Location"; var location = GetCurrentLocation(); var parameter = Expression.Parameter(entityType, "entity"); var lambda = Expression.Lambda( Expression.Equal( Expression.Property(parameter, propertyName), Expression.Constant(location) ) , parameter); </code></pre> <p>I get an error that says:</p> <p><code>Unable to create a constant value of type 'Location'. Only primitive types or enumeration types are supported in this context.</code></p> <p>My suspicion is that <code>Expression.Constant()</code> only expects primitive types, so I need to use a different expression factory method. (maype <code>Expression.Object</code>? - I know that doesn't exist)</p> <p>Is there a way to create an expression that compares objects? Why is that EF is able to interpret it correctly if its a compiled LINQ statement, but not when it is an expression?</p>
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