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POHow to convert a String to its equivalent LINQ Expression Tree?
 

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  1. POHow to convert a String to its equivalent LINQ Expression Tree?
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    <p>This is a simplified version of the original problem.</p> <p>I have a class called Person:</p> <pre><code>public class Person { public string Name { get; set; } public int Age { get; set; } public int Weight { get; set; } public DateTime FavouriteDay { get; set; } } </code></pre> <p>...and lets say an instance:</p> <pre><code>var bob = new Person { Name = "Bob", Age = 30, Weight = 213, FavouriteDay = '1/1/2000' } </code></pre> <p>I would like to write the following as a <em>string</em> in my favourite text editor....</p> <pre><code>(Person.Age &gt; 3 AND Person.Weight &gt; 50) OR Person.Age &lt; 3 </code></pre> <p>I would like to take this string and my object instance and evaluate a TRUE or FALSE - i.e. evaluating a Func&lt;Person, bool> on the object instance.</p> <p>Here are my current thoughts:</p> <ol> <li>Implement a basic grammar in ANTLR to support basic Comparison and Logical Operators. I am thinking of copying the Visual Basic precedence and some of the featureset here: <a href="http://msdn.microsoft.com/en-us/library/fw84t893(VS.80).aspx" rel="noreferrer">http://msdn.microsoft.com/en-us/library/fw84t893(VS.80).aspx</a></li> <li>Have ANTLR create a suitable AST from a provided string.</li> <li>Walk the AST and use the <a href="http://www.albahari.com/nutshell/predicatebuilder.aspx" rel="noreferrer">Predicate Builder</a> framework to dynamically create the Func&lt;Person, bool></li> <li>Evaluate the predicate against an instance of Person as required</li> </ol> <p><strong>My question is have I totally overbaked this? any alternatives?</strong></p> <hr> <h2>EDIT: Chosen Solution</h2> <p>I decided to use the Dynamic Linq Library, specifically the Dynamic Query class provided in the LINQSamples.</p> <p>Code below:</p> <pre><code>using System; using System.Linq.Expressions; using System.Linq.Dynamic; namespace ExpressionParser { class Program { public class Person { public string Name { get; set; } public int Age { get; set; } public int Weight { get; set; } public DateTime FavouriteDay { get; set; } } static void Main() { const string exp = @"(Person.Age &gt; 3 AND Person.Weight &gt; 50) OR Person.Age &lt; 3"; var p = Expression.Parameter(typeof(Person), "Person"); var e = System.Linq.Dynamic.DynamicExpression.ParseLambda(new[] { p }, null, exp); var bob = new Person { Name = "Bob", Age = 30, Weight = 213, FavouriteDay = new DateTime(2000,1,1) }; var result = e.Compile().DynamicInvoke(bob); Console.WriteLine(result); Console.ReadKey(); } } } </code></pre> <p>Result is of type System.Boolean, and in this instance is TRUE.</p> <p>Many thanks to Marc Gravell.</p> <p>Include <a href="https://www.nuget.org/packages/System.Linq.Dynamic/" rel="noreferrer">System.Linq.Dynamic</a> nuget package, documentation <a href="https://github.com/kahanu/System.Linq.Dynamic/wiki/Dynamic-Expressions" rel="noreferrer">here</a></p>
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    1. COThanks for posting the full solution code along with your question. Much appreciated.
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    2. COwhat if you have a collection or people and would like to filter some elements? Person.Age > 3 AND Person.Weight > 50 ?
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