List<object>.Contains Expression Tree
Question
I would like to build an Expression that would equate to expected...
Expression<Func<ReferencedEntity, bool>> expected = (ReferencedEntity referencedEntity) => foreignKeys.Contains(referencedEntity.Id);
Expression<Func<ReferencedEntity, bool>> actual;
foreignKeys type is a List<object>
Here is what I have so far and I think it would use Expression.Call() method but not sure exactly how to go about it.
ParameterExpression entityParameter = Expression.Parameter(typeof(TReferencedEntity), "referencedEntity");
MemberExpression memberExpression = Expression.Property(entityParameter, "Id");
Expression convertExpression = Expression.Convert(memberExpression, typeof(object)); //This is becuase the memberExpression for Id returns a int.
//Expression containsExpression = Expression.Call(????
//actual = Expression.Lambda<Func<TReferencedEntity, bool>>(????, entityParameter);
Thanks for you help.
Solution
Here is the solution I couldn't have done it without Samuel's suggestion though...
/// <summary>
///
/// </summary>
/// <param name="foreignKeys"></param>
/// <returns></returns>
private Expression<Func<TReferencedEntity, bool>> BuildForeignKeysContainsPredicate(List<object> foreignKeys, string primaryKey)
{
Expression<Func<TReferencedEntity, bool>> result = default(Expression<Func<TReferencedEntity, bool>>);
try
{
ParameterExpression entityParameter = Expression.Parameter(typeof(TReferencedEntity), "referencedEntity");
ConstantExpression foreignKeysParameter = Expression.Constant(foreignKeys, typeof(List<object>));
MemberExpression memberExpression = Expression.Property(entityParameter, primaryKey);
Expression convertExpression = Expression.Convert(memberExpression, typeof(object));
MethodCallExpression containsExpression = Expression.Call(foreignKeysParameter
, "Contains", new Type[] { }, convertExpression);
result = Expression.Lambda<Func<TReferencedEntity, bool>>(containsExpression, entityParameter);
}
catch (Exception ex)
{
throw ex;
}
return result;
}
OTHER TIPS
I don't know the solution, but I know how you could get it. Create a dummy function that takes in an Expression<Func<ReferencedEntity, bool>>
and pass it your lambda. And using a debugger you can examine how the compiler created the expression for you.
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