Generating expressions at runtime

Delegate.cs

var containers = new[]
{
    new Container { Value = "bag" },
    new Container { Value = "bed" },
    new Container { Value = "car" }
};

var filteredResults =
    containers.Where(container => container.Value.Contains("a"))

ExpressionTree.cs

var containers = new[]
{
    new Container { Value = "bag" },
    new Container { Value = "bed" },
    new Container { Value = "car" }
};

// The parameter of the lambda expression 
var argument = Expression.Parameter(typeof(Container));

// The "Value" property of the previously-declared parameter
var valueProperty = Expression.Property(argument, "Value");

// The Contains method represented as an expression tree 
var containsCall = Expression.Call(
    // Call the method on the "Value" property.
    valueProperty,
    // The method you want to call on the property
    typeof(string).GetMethod(
        "Contains", 
        new[] { typeof(string) }
    ),
    // The argument to pass to the "Contains" method.
    Expression.Constant("a", typeof(string))
);

// Lambda expression to pass into the Where method
var wherePredicate =
    Expression.Lambda<Func<Container, bool>>(
        containsCall, 
        argument
    );

// Invoke the Where method on the queryable object itsself
var whereCall = 
    Expression.Call(
        typeof(Queryable), 
        "Where",
        new[] { typeof(Container) },
        containers.AsQueryable().Expression, 
        wherePredicate
    );

var expressionResults =
    containers.AsQueryable().Provider.CreateQuery<Container>(whereCall);