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POmanually build linq expression for x => x.Child == itemToCompare.Child
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  1. POmanually build linq expression for x => x.Child == itemToCompare.Child
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    copied!<p>We have an object and we want to build a linq query based on that object on the fly. This linq statement is equivalent to what we want to build:</p> <pre><code>Expression&lt;Func&lt;Sample, bool&gt;&gt; linqExpression = x =&gt; x.Child == itemToCompare.Child; </code></pre> <p>We can't quite come up with the right expression to build the itemToCompare.Child part. Here's what we have so far:</p> <pre><code>var param = Expression.Parameter(typeof(T), "x"); var key = itemToCompare.GetType().GetProperty("Child"); var rhsConstant = Expression.Constant(item); var innerLambda = Expression.Lambda&lt;Func&lt;T&gt;&gt;(rhsConstant, new ParameterExpression[0]); var rhsMemberAccess = Expression.MakeMemberAccess(innerLambda, key); body = Expression.Equal(lhsPropertyAccess, rhsMemberAccess); var lambda = Expression.Lambda&lt;Func&lt;T, bool&gt;&gt;(body, param); </code></pre> <p>The expression tree for our hand-built query looks like:</p> <pre><code>Lambda Expression: x =&gt; (x.Child = value(SampleTests+Sample)) Expression Body: (x.Child = value(SampleTests+Sample)) Parameter 0: 'x', Type: Sample NodeType: Lambda Left Lambda Expression: x.Child Left NodeType: MemberAccess Lambda Expression: x Expression Member: Sample Child NodeType: Parameter -- a parameter expression Right Lambda Expression: value(SampleTests+Sample) Right NodeType: Constant NodeType: Constant Value: SampleTests+Sample </code></pre> <p>The expression tree for the actual lambda looks like:</p> <pre><code>Lambda Expression: x =&gt; (x.Child = value(SampleTests+&lt;&gt;c__DisplayClass15).itemToCompare.Child) Expression Body: (x.Child = value(SampleTests+&lt;&gt;c__DisplayClass15).itemToCompare.Child) Parameter 0: 'x', Type: Sample NodeType: Lambda Left Lambda Expression: x.Child Left NodeType: MemberAccess Lambda Expression: x Expression Member: Sample Child NodeType: Parameter -- a parameter expression Right Lambda Expression: value(SampleTests+&lt;&gt;c__DisplayClass15).itemToCompare.Child Right NodeType: MemberAccess Lambda Expression: value(SampleTests+&lt;&gt;c__DisplayClass15).itemToCompare Expression Member: Sample Child NodeType: MemberAccess Lambda Expression: value(SampleTests+&lt;&gt;c__DisplayClass15) Expression Member: Sample itemToCompare NodeType: Constant NodeType: Constant Value: SampleTests+&lt;&gt;c__DisplayClass15 </code></pre> <p>Edit:</p> <p>We think this works out to</p> <pre><code>Expression&lt;Func&lt;Sample, bool&gt;&gt; linqExpression = x =&gt; x.Child == (()=&gt;itemToCompare).Child; </code></pre> <p>which is what we're trying to reproduce in our expression. </p> <p>Ultimately the goal is to produce an Expression where the Child values are compared using their Type's .Equals() method.</p> <p>Thanks!</p>
 

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