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POHow to convert Expression<Func<T, bool>> to Expression<Func<Type, bool>>?
 

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  1. POHow to convert Expression<Func<T, bool>> to Expression<Func<Type, bool>>?
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    <p>I am trying build a dictionary of Expressions that have different input parameter types. I am trying to store the type of the parameter because later down the road I plan to use Reflection to discover a method on the type. Here is the code that creates the dictionary and a generic Add function I created to add entries to it:</p> <pre><code>public class LoadEntityQuery : IQuery&lt;LoadEntityQueryResult&gt; { public IDictionary&lt;Type, Expression&lt;Func&lt;Type, bool&gt;&gt;&gt; Entities { get; set; } public LoadEntityQuery() { Entities = new Dictionary&lt;Type, Expression&lt;Func&lt;Type, bool&gt;&gt;&gt;(); } public void Add&lt;T&gt;(Expression&lt;Func&lt;T, bool&gt;&gt; where = null) where T : Entity { Expression&lt;Func&lt;Type, bool&gt;&gt; _lambda = null; if (where != null) { ParameterExpression param = Expression.Parameter(typeof(T), where.Parameters[0].Name); var body = Expression.Invoke(where, param); _lambda = Expression.Lambda&lt;Func&lt;Type, bool&gt;&gt;(body, param); } Entities.Add(typeof(T), _lambda); } } </code></pre> <p>The body of the new method is created properly. The issue is when I try to create the new Lambda expression with the type from the expression being passed in, I receive this error:</p> <p>ParameterExpression of type 'TestNamespace.TestClass' cannot be used for delegate parameter of type 'System.Type'</p> <p>Does anybody have an idea as to what I can do in this situation? Like I said before, at some point later I am going to loop through this dictionary to do some reflective programming on each entry. If there is a better way to do this I am all ears.</p> <p>As an example of what I am trying to do, I store the expressions for Where clauses for POCO objects that need to be initialized:</p> <pre><code>LoadEntityQuery _query = new LoadEntityQuery(); _query.Add&lt;PayrollLocation&gt;(); _query.Add&lt;PayrollGroupBU&gt;(); _query.Add&lt;PersonnelPosition&gt;(t =&gt; t.DataSet == MasterDataSet); _query.Add&lt;EmployeeStatus&gt;(); _query.Add&lt;PayrollGrade&gt;(); </code></pre> <p>This list of Entities will be different for each app. The idea is to collect all the entities and Where clause for each and discover a certain method using reflection on each one. (e.g. PayrollLocation has a GetPayrollLocationsQuery() method, PayrollGroupBU has a GetPayrollGroupBUQuery() method...). The Add method is generic in order for me to make use of the lambda expression in the calling code.</p> <p>Thanks, Jason</p>
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