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POLinq query with Contains only works with is IQueryable is in external variable
 

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  1. POLinq query with Contains only works with is IQueryable is in external variable
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    <p>I am using Entity Framework with Linq to Entities, trying to select some data from my database. When I create a Linq query that uses the method <code>IQueryable&lt;int&gt;.Contains</code>, it can only filter the data if I use an external variable! Let me show some example.</p> <p>This block of code, <strong>works perfectly</strong>:</p> <pre><code>var volumes = (from v in work.VolumeAdditiveRepository.All where v.AdditivesID == AdditivesID select v.MetricID); var metrics = from m in work.MetricRepository.All where !volumes.Contains(m.ID) select m; </code></pre> <p>If you take a good look, you can see I use the variable <code>volumes</code> inside this snippet, in the <code>where</code> condition. If I copy the contents of this variable and paste it inside the <code>metrics</code> variable, leading to the code below, it raises the error: <code>"Unable to create a constant value of type 'CalculadoraRFS.Models.Domain.VolumeAditivo'. Only primitive types ('such as Int32, String, and Guid') are supported in this context."</code>.</p> <pre><code>var metrics = from m in work.MetricRepository.All where !(from v in work.VolumeAdditiveRepository.All where v.AdditivesID == AdditivesID select v.MetricID).Contains(m.ID) select m; </code></pre> <p>How can I variable substitution cause such error?! Am I doing (certainly) something wrong?<br> Thank you!</p> <hr> <p><strong>UPDATE:</strong></p> <p>Actually, I find out that the Repository Pattern or DbContext seems to be the problem, as @jhamm pointed out. The snippet below doesn't work either:</p> <pre><code>var query = from m in work._context.Metric where !(from v in work._context.VolumeAdditive where v.AdditivesID == AdditivesID select v.MetricID).Contains(m.ID) select m; </code></pre> <p>But the snippet below works. I just took the context out of the UnitOfWork class, though it is very simply defined there: <code>public CalculadoraRFSContext _context = new CalculadoraRFSContext();</code>.</p> <pre><code>var _context = new CalculadoraRFSContext(); var query = from m in _context.Metric where !(from v in _context.VolumeAdditive where v.AdditivesID == AdditivesID select v.MetricID).Contains(m.ID) select m; </code></pre> <p>Now I'm really confused about this stuff! Wasn't it supposed to work as expected?!</p>
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