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    <p>Your Address class already has a State property that represents the relation. Why don't you just use that?</p> <pre><code>public IQueryable&lt;string&gt; Addresses() { var query = from a in _contextProvider.Context.Addresses where a.CityName.StartsWith("I") select a.State.StateName; return query; } </code></pre> <hr> <p><strong>Update:</strong></p> <p>From your latest comment I guess you turned off lazy loading for your model by setting <code>LazyLoadingEnabled</code> to false. By default lazy loading is enabled which can be a bit confusing since older versions of EF didn't even support lazy loading.</p> <p>Disabling lazy loading "activates" explicit loading and unsurprisingly requires you to explicitly load related objects. In your case you can do this by either using the <code>Include</code> method (this is called eager loading):</p> <pre><code>var query = from a in _contextProvider.Context.Addresses.Include("State") where a.CityName.StartsWith("I") select a; </code></pre> <p>or access the related property in query (which modifies the final query):</p> <pre><code>var states = (from a in Addresses() // Addresses is your query method select a.State).ToList(); </code></pre> <p>In the second version linq-to-entities automatically includes the states because you are accessing them in the query. Note that your <code>Addresses</code> method returns an <code>IQueryable</code> and therefore the query will not be executed before you actually enumerate it. So the executed SQL query very much depends on how you use the query returned by <code>Addresses</code>.</p> <p>If you first execute the <code>Addresses</code> query and access the states later linq-to-entities will not include them:</p> <pre><code>var states = (from a in Addresses().ToList() // &lt;- ToList() executes the query before states are accessed select a.State).ToList(); </code></pre> <p>Lazy loading is often turned off to avoid unneeded roundtrips to the database. If you enable lazy loading and then immediately execute the query returned by <code>Addresses</code> each access to a related object will actually produce a database query. But again: if you include the states in the final query linq-to-entities will automatically include them by generating a JOIN (no matter if you use lazy loading or not).</p> <p>So your solution to use <code>Include</code> to eagerly load related states (even if you don't access them later) is ok. And your original idea to use a join is also ok. But since you want your method to return an <code>IQueryable&lt;Address&gt;</code> you have to do it on the call site (as described above).</p> <p>From my experience enabling lazy loading often makes things a lot easier. If you don't know exactly what's going on it can result in a lot of unnecessary roundtrips to the database. But you can still use <code>Include</code> to optimize your queries. To better understand how LINQ queries get translated into SQL statements I recommend to use SQL Profiler (or a free tool like <a href="http://expressprofiler.codeplex.com/" rel="nofollow noreferrer">Express Profiler</a> if you use SQL Server Express).</p> <p>On the other hand using explicit loading can also be a pain. Being forced to include all related tables can result in <a href="https://stackoverflow.com/questions/5521749/how-many-include-i-can-use-on-objectset-in-entityframework-to-retain-performance">huge datasets</a>. If for some reasons you can not include all related tables you have to explicitly check if an entity is loaded: <code>context.Entry(address).Reference(a =&gt; a.State).IsLoaded</code>. If a nullable property is null you don't know if it is NULL in the database or just not yet loaded.</p>
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    1. POSimple LINQ join to return IQueryable collection of objects
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    1. COThat gives me a conversion error, (Cannot implicitly convert type 'System.Linq.IQueryable<string>' to 'System.Linq.IQueryable<Project.Models.Address>'), and I understand why. I want all the Address fields, not just the state name. Do I have to explicitly list them? And then will I have to cast it? Thanks
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    2. CO@mwill: I changed the return type to `IQueryable<string>`. If you want to get all Address fields then your code is perfectly ok. The JOIN is already done through the ForeignKey attribute of the State property.
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    3. COYes, I want all the address fields. In my original code, the State is NULL so I thought I had to write the join myself. Maybe there's a setting that I'm missing somewhere? thanks
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