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POLINQ to SQL - mapping exception when using abstract base classes
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  1. POLINQ to SQL - mapping exception when using abstract base classes
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    copied!<p>Problem: I would like to share code between multiple assemblies. This shared code will need to work with LINQ to SQL-mapped classes.</p> <p>I've encountered the same issue found <a href="https://stackoverflow.com/questions/156113/linqtosql-and-abstract-base-classes">here</a>, but I've also found a work-around that I find troubling (I'm not going so far as to say "bug").</p> <p><strong>All the following code can be downloaded in <a href="http://www.filehosting.org/file/details/40226/TestLinq2Sql.zip" rel="nofollow noreferrer">this solution</a>.</strong></p> <p>Given this table:</p> <pre><code>create table Users ( Id int identity(1,1) not null constraint PK_Users primary key , Name nvarchar(40) not null , Email nvarchar(100) not null ) </code></pre> <p>and this DBML mapping:</p> <pre><code>&lt;Table Name="dbo.Users" Member="Users"&gt; &lt;Type Name="User"&gt; &lt;Column Name="Id" Modifier="Override" Type="System.Int32" DbType="Int NOT NULL IDENTITY" IsPrimaryKey="true" IsDbGenerated="true" CanBeNull="false" /&gt; &lt;Column Name="Name" Modifier="Override" Type="System.String" DbType="NVarChar(40) NOT NULL" CanBeNull="false" /&gt; &lt;Column Name="Email" Modifier="Override" Type="System.String" DbType="NVarChar(100) NOT NULL" CanBeNull="false" /&gt; &lt;/Type&gt; &lt;/Table&gt; </code></pre> <p>I've created the following base classes in one assembly "Shared":</p> <pre><code>namespace TestLinq2Sql.Shared { public abstract class UserBase { public abstract int Id { get; set; } public abstract string Name { get; set; } public abstract string Email { get; set; } } public abstract class UserBase&lt;TUser&gt; : UserBase where TUser : UserBase { public static TUser FindByName_Broken(DataContext db, string name) { return db.GetTable&lt;TUser&gt;().FirstOrDefault(u =&gt; u.Name == name); } public static TUser FindByName_Works(DataContext db, string name) { return db.GetTable&lt;TUser&gt;().FirstOrDefault(u =&gt; u.Name == name &amp;&amp; 1 == 1); } public static TUser FindByNameEmail_Works(DataContext db, string name, string email) { return db.GetTable&lt;TUser&gt;().FirstOrDefault(u =&gt; u.Name == name || u.Email == email); } } } </code></pre> <p>These classes are referenced in another assembly "Main", like so:</p> <pre><code>namespace TestLinq2Sql { partial class User : TestLinq2Sql.Shared.UserBase&lt;User&gt; { } } </code></pre> <p>The DBML file is located in the "Main" assembly, as well.</p> <p>When calling <code>User.FindByName_Broken(db, "test")</code>, an exception is thrown:</p> <blockquote> <p>System.InvalidOperationException: Class member UserBase.Name is unmapped.</p> </blockquote> <p>However, the other two base static methods work. </p> <p>Furthermore, the SQL generated by calling <code>User.FindByName_Works(db, "test")</code> is what we were hoping for in the broken call:</p> <pre><code>SELECT TOP (1) [t0].[Id], [t0].[Name], [t0].[Email] FROM [dbo].[Users] AS [t0] WHERE [t0].[Name] = @p0 -- @p0: Input NVarChar (Size = 4; Prec = 0; Scale = 0) [test] </code></pre> <p>While I am willing to use this <code>1 == 1</code> "hack" for single predicate queries, is there a better way of sharing LINQ to SQL-aware code in a base/shared/core assembly?</p>
 

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