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POPerformance difference with MemberInit Expression
 

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  1. POPerformance difference with MemberInit Expression
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    <p>I am working a similar problem as <a href="https://stackoverflow.com/questions/222511/refactor-to-eliminate-repetition-in-lamba-expression">Question 222511</a> I do need to use the MemberInit Expression so I can just add them to the constructor... I am trying to implement <a href="https://stackoverflow.com/users/22656/jon-skeet">John Skeet's</a> answer but I am running into a big performance difference. Here is some of the code:</p> <pre><code>// Method A: // This work good, is fast and returns an un-executed query... DataContext.LoanNote.Join&lt;LoanNote, Customer, int, LoanNote&gt;( DataContext.Customers, loanNote =&gt; loanNote.PrimaryCustomerNumber, customer =&gt; customer.CustomerNumber, (LoanNote loanNote, Customer customer) =&gt; new LoanNote() { AccountFeeBillAmount = loanNote.AccountFeeBillAmount, AccountOpenDate = loanNote.AccountOpenDate, // This goes on and on... PrimaryCustomer = customer }); // Method B: // This on the other hand is a lot slower and I am not sure why... var resultSelector = BuildJoinResultSelector&lt;LoanNote, Customer, LoanNote("PrimaryCustomer").Compile(); DataContext.LoanNote.Join&lt;LoanNote, Customer, int, LoanNote&gt;( DataContext.Customers, loanNote =&gt; loanNote.PrimaryCustomerNumber, customer =&gt; customer.CustomerNumber, resultSelector); // The build MemberInitExpression method... private static Expression&lt;Func&lt;TOuter, TInner, TResult&gt;&gt; BuildJoinResultSelector&lt;TOuter, TInner, TResult&gt;(string propertyName) where TResult : class { var result = default(Expression&lt;Func&lt;TOuter, TInner, TResult&gt;&gt;); var resultType = typeof(TResult); var outerType = typeof(TOuter); var innerType = typeof(TInner); var outer = Expression.Parameter(outerType, "outer"); var inner = Expression.Parameter(innerType, "inner"); var bindings = new List&lt;MemberBinding&gt;(); foreach (var property in resultType.GetProperties()) { if (property.CanRead == false) { continue; } else if (property.CanWrite == false) { continue; } else if (property.Name == propertyName) { var condition = Expression.Condition(Expression.Equal(inner, Expression.Constant(null)), Expression.New(innerType), inner); bindings.Add(Expression.Bind(property, condition)); } else { bindings.Add(Expression.Bind(property, Expression.Property(outer, property))); } } var memberInit = Expression.MemberInit(Expression.New(resultType), bindings); result = Expression.Lambda&lt;Func&lt;TOuter, TInner, TResult&gt;&gt;(memberInit, outer, inner); return result; } </code></pre>
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    1. COYou have a typo in your title (performa*n*ce)
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    2. COCan you post the entire code for method A?
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    3. COIt's just more Property Init's ex: Balance = loanNote.Balance, APR = loanNote.APR, etc...
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