Can Dynamic LINQ Queries Be Built from XML Configuration?

Dynamic LINQ Queries from XML Configuration

Question:

Can we construct LINQ queries dynamically without altering the source code? In this scenario, query parameters would be extracted from an XML configuration stored in the database.

Example:

var result = from i in someObj
             where name = 'Bob'

Dynamic Query Generation:

Answer:

Expression trees offer a solution for this dynamic query generation. Here's a code example:

var param = Expression.Parameter(typeof(SomeObject), "p");
var exp = Expression.Lambda<Func<SomeObject, bool>>(
    Expression.Equal(
        Expression.Property(param, "Name"),
        Expression.Constant("Bob")
    ),
    param
);
var query = someObj.Where(exp);

Explanation:

• param defines a parameter of type SomeObject.
• Expression.Lambda creates a lambda expression that represents the LINQ query.
• Expression.Equal compares the Name property of the SomeObject to the constant Bob.
• Finally, someObj.Where(exp) applies the expression to the someObj collection, resulting in a dynamic LINQ query.

Note: This approach is more complex but provides flexibility for situations where dynamic query construction is essential from an XML configuration.

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