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POLINQ, Large filter on a query
 

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    <p>I am building a section of an application that revolves around pulling information about transactions out of the database. Due to the nature of the data, there are many columns in the table that I want to filter on. I have a filter selection box with 15 fields that I want to be able to build up a where clause for the LINQ statement. The interesting part comes when I want certain fields to be null. For example I want to be able to filter on any or all of:</p> <ul> <li>Transaction Type</li> <li>Response Code</li> <li>Transaction Amount</li> <li>Many more</li> </ul> <p>I can build up a predicate that looks like</p> <pre><code>Func&lt;Transaction, bool&gt; pred = t =&gt; t.ResponseCode == ResponseCode &amp;&amp; t.TransactionType == TransactionType &amp;&amp; t.TransactionAmount &gt; 100.00; </code></pre> <p>But in order to be able to choose which fields to include in the predicate I am <a href="https://stackoverflow.com/questions/491780/concatenating-lambda-functions-in-c">concatenating the predicates</a> together:</p> <pre><code>Func&lt;Transaction, bool&gt; pred = t =&gt; true; if(ResponseCode != null) pred.AndAlso(t =&gt; t.ResponseCode == ResponseCode); // Rinse and repeat </code></pre> <p>And then passing that predicate to the where clause of the LINQ statement.</p> <p>This works exactly the way I want it, but is rather complicated. Are there any other ways of doing this?</p> <p>UPDATE: Thanks Justice for the comments. I'm not using LINQ to SQL, I'm using LINQ on a collection of objects from a repository. How would you programatically build an Expression filter?</p>
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    1. USJohn Oxley
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    1. COIf you're using LinqToObjects (methods on System.Linq.Enumerable), you don't need to worry about Expression<Func<T, bool>>. Instead use Func<T, bool>.
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    2. COI thought you were using LINQ to SQL based on you talking about pulling data from a database.
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      1. USyfeldblum
 

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