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POLINQ - Place part of a query that is always the same in a separate class and use in other linq queries
 

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  1. POLINQ - Place part of a query that is always the same in a separate class and use in other linq queries
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    <p><strong>Current situation</strong></p> <p>Currently I have this <code>Linq</code> query:</p> <pre><code>return from function in this.context.Functions join fp in this.context.FunctionParameters on function.FunctionID equals fp.FunctionID into functionParameters from functionParameter in functionParameters.DefaultIfEmpty() join d in this.context.Descriptions on new { ID = (int)function.FunctionID, languageID = languageID, originID = (byte)origin } equals new { ID = d.ValueID, languageID = d.LanguageID, originID = d.OriginID } into entityWithDescription from x in entityWithDescription.DefaultIfEmpty() select new FunctionDTO() { Function = function, Description = x }; </code></pre> <p>This returns the functions with their parameters and the specific descriptions. So, a select with two left outer joins. This is all good and works.</p> <p><strong>The problem</strong></p> <p>I have multiple objects that have a description. The description table has no relationship with these objects (so no FK). So there is a part of the above query that is <strong>always</strong> the same, namely the join query to the description table:</p> <pre><code>join d in this.context.Descriptions on new { ID = (int)function.FunctionID, languageID = languageID, originID = (byte)origin } equals new { ID = d.ValueID, languageID = d.LanguageID, originID = d.OriginID } into entityWithDescription </code></pre> <p>The variables <code>languageID</code> and <code>origin</code> are two parameters that are passed on with the method. The <code>FunctionID</code> is a property in my <code>Function</code> class, ie a property in my <code>entity model</code>. So that is a </p> <pre><code>public partial class Function { public byte FunctionID { get; set; } /** Other properties **/ } </code></pre> <p><strong>My question</strong></p> <p>Is it possible to create a separate class with the part of the <code>linq</code> query that is always the same? So that I don't have to duplicate the same code all over again? </p> <p><strong>What I already tried</strong></p> <pre><code>var query = from function in this.context.Functions join fp in this.context.FunctionParameters on function.FunctionID equals fp.FunctionID into functionParameters from functionParameter in functionParameters.DefaultIfEmpty() select function; var testResult = this.context.Descriptions.GetDescriptionsByJoin(query, languageID, origin); </code></pre> <p>And the duplicate code in a separate class:</p> <pre><code>public static IQueryable&lt;IEnumerable&lt;Description&gt;&gt; GetDescriptionsByJoin( this IDbSet&lt;Description&gt; descriptions, IQueryable&lt;ITranslatable&gt; query, byte languageID, OriginEnum origin) { return from q in query join d in descriptions on new { ID = q.ValueID, languageID = languageID, originID = (byte)origin } equals new { ID = d.ValueID, languageID = d.LanguageID, originID = d.OriginID } into entityWithDescription select entityWithDescription; } </code></pre> <p>But this gave me the following error:</p> <pre><code>The specified type member is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported </code></pre> <p>I know that I get this error because I use my 'valueID' as a parameter in my join statement and that variable can't be found in my entity model (valueID is a property in an interface 'ITranslatable' that all my classes that have descriptions will implement).</p> <p>Thanks in advance!</p> <p>Greetings Loetn</p>
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    1. USLoetn
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      1. POLINQ - Place part of a query that is always the same in a separate class and use in other linq queries
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    1. COHave you looked at LinqKit? It's on nuget.
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      1. USdanludwig
 

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