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POConstruct a LINQ GroupBy query using expression trees
 

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    <p>I have stuck on this problem for a week and no solution found.</p> <p>I have a POCO like below:</p> <pre class="lang-cs prettyprint-override"><code>public class Journal { public int Id { get; set; } public string AuthorName { get; set; } public string Category { get; set; } public DateTime CreatedAt { get; set; } } </code></pre> <p>I want to know during a specific date span ( grouped by months or years ) the amount of journals count by a AuthorName or a Category.</p> <p>After I send the queryed object to JSON serializer then generated JSON data like below ( just using JSON to demonstrate the data I want to get, how to serializer a object to a JSON is not my problem )</p> <pre><code>data: { '201301': { 'Alex': 10, 'James': 20 }, '201302': { 'Alex': 1, 'Jessica': 9 } } </code></pre> <p>OR</p> <pre><code>data: { '2012': { 'C#': 230 'VB.NET': 120, 'LINQ': 97 }, '2013': { 'C#': 115 'VB.NET': 29, 'LINQ': 36 } } </code></pre> <p>What I know is to write a LINQ query in "method way" like:</p> <pre class="lang-cs prettyprint-override"><code>IQueryable&lt;Journal&gt; query = db.GroupBy(x=&gt; new { Year = key.CreatedAt.Year, Month = key.CreatedAt.Month }, prj =&gt; prj.AuthorName) .Select(data =&gt; new { Key = data.Key.Year * 100 + data.Key.Month, // very ugly code, I know Details = data.GroupBy(y =&gt; y).Select(z =&gt; new { z.Key, Count = z.Count() }) }); </code></pre> <p>The conditions that grouped by months or years, AuthorName or Category will be passed by two string type method parameters. What I don't know is how to use "Magic String" parameters in a GroupBy() method . After some googling, it seems that I cannot group data by passing a magic string like "AuthorName". What I should to do is build a expression tree and pass it to the GroupBy() method.</p> <p>Any solution or suggestion is appreciate.</p>
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    1. COHave you looked at dynamic LINQ?
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    2. CO@svick If I have another option beside LINQ to Entity, I will choose StackOverflow's Dapper rather than dynamic LINQ
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    3. CODynamic LINQ works on top of `IQueryable`, so it doesn't replace libraries like LINQ to Entities, it actually requires some library like that to work.
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