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POIs there a secret to using LINQ to SQL to add records when the object has relationships?
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  1. POIs there a secret to using LINQ to SQL to add records when the object has relationships?
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    copied!<p>I am working in LINQ to SQL, ASP.NET MVC, and C#. I have a repository called <code>genesisRepository</code> to connect to the database. </p> <p>I have a table represented in an object called Stream. It is defined like this:</p> <pre><code>[Table] public class Stream { [HiddenInput(DisplayValue = false)] [Column(IsPrimaryKey = true, IsDbGenerated = true, AutoSync = AutoSync.OnInsert)] public long StreamID { get; set; } [Required(ErrorMessage = "Please enter a stream name")] [Column] public string StreamName { get; set; } /* Other columns removed for brevity */ [Required(ErrorMessage = "Please enter a stream URL")] [Column] public string StreamUrl { get; set; } private EntitySet&lt;StreamEntry&gt; _StreamEntry; [System.Data.Linq.Mapping.Association(Storage = "_StreamEntry", OtherKey = "StreamID")] public EntitySet&lt;StreamEntry&gt; StreamEntry { get { return this._StreamEntry; } set { this._StreamEntry.Assign(value); } } private EntitySet&lt;Stream2FieldTypes&gt; _Stream2FieldTypes; [System.Data.Linq.Mapping.Association(Storage = "_Stream2FieldTypes", OtherKey = "StreamID")] public EntitySet&lt;Stream2FieldTypes&gt; Stream2FieldTypes { get { return this._Stream2FieldTypes; } set { this._Stream2FieldTypes.Assign(value); } } } </code></pre> <p>I have a test action in my controller for creating new records inside my <code>Stream</code> table.</p> <pre><code> public ActionResult StreamTest() { // create new stream var stream = new Genesis.Domain.Entities.Stream(); stream.StreamUrl = "url"; stream.StreamName = "name"; stream.StreamBody = null; stream.StreamTitle = null; stream.StreamKeywords = null; stream.StreamDescription = null; genesisRepository.CreateStream(stream); return View("Index"); } </code></pre> <p>The function <code>genesisRepository()</code> looks like this:</p> <pre><code> public long CreateStream(Stream stream) { streamTable.InsertOnSubmit(stream); streamTable.Context.SubmitChanges(); return stream.StreamID; } </code></pre> <p>I get a null reference error when I execute the ActionResult <code>StreamTest()</code>. genesisRepository is not null. <code>streamTable</code> is not null, and the newly create object <code>stream</code> is also obviously not null. The only thing I can think of that would be null are the <code>EntitySet&lt;T&gt;</code> properties which define the foreign relationships.</p> <p>So, I modified the ActionResult code to be this:</p> <pre><code> public ActionResult StreamTest() { // create new stream var stream = new Genesis.Domain.Entities.Stream(); stream.Stream2FieldTypes = new EntitySet&lt;Stream2FieldTypes&gt;(); // new stream.StreamEntry = new EntitySet&lt;StreamEntry&gt;(); // new stream.StreamUrl = "url"; stream.StreamName = "name"; stream.StreamBody = null; stream.StreamTitle = null; stream.StreamKeywords = null; stream.StreamDescription = null; genesisRepository.CreateStream(stream); // CreateStream() returns ID as long return View("Index"); } </code></pre> <p>But when I tried that, I got this error:</p> <pre><code>Exception Details: System.NullReferenceException: Object reference not set to an instance of an object. Source Error: Line 58: { Line 59: get { return this._Stream2FieldTypes; } Line 60: set { this._Stream2FieldTypes.Assign(value); } &lt;-- the offending line Line 61: } Line 62: Source File: C:\path\to\Stream.cs Line: 60 </code></pre> <p>I can create a new record using <code>streamTable.Context.ExecuteCommand("INSERT INTO genesis.dbo.Stream (StreamName, StreamUrl) VALUES ('Name', 'url');");</code>.</p> <p>I don't understand how to move forward from here. How can I simply create a new record in <code>Stream</code>?</p>
 

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