CODEWITHSUNDEEP
c#iqueryable
LukeP
LukeP

Reputation: 10422

How to remove or overwrite where clause in existing IQueryable

Assuming the following prefiltered IQueryable:

var query = items.Where(i => i.PropertyName == "Some property");

coming from a third party library, is it possible to either remove the Where clause completely, or replace it with:

.Where(i => i.PropertyName == null || i.PropertyName == "Some property")

I've seen mentions of being able to rewrite the IQueryable on the fly. Would this approach have any downsides? How would I go about doing it? Is there a better way?

Update

I've managed to cobble something together using ExpressionVisitor as suggested by Ivan:

public class WhereRemoveVisitor : ExpressionVisitor
{
    protected override Expression VisitMethodCall(MethodCallExpression node)
    {
        if (node.Method.Name == "Where" && node.Method.DeclaringType == typeof(Queryable))
            return node.Arguments[0];
        else
            return base.VisitMethodCall(node);
    }
}

and:

public static class IQueryableExtensions
{
    public static IQueryable<T> RemoveWhere<T>(this IQueryable<T> expression)
    {
        return Expression.Lambda<IQueryable<T>>(new WhereRemoveVisitor().Visit(expression.Expression)).Compile();
    }
}

While this compiles fine, it throws "Lambda type parameter must be derived from System.Delegate" in the extension method.

Upvotes: 3

Views: 1316

Answers (1)

LukeP
LukeP

Reputation: 10422

I've managed to put something together using ExpressionVisitor as suggested by Ivan:

public class WhereRemoveVisitor : ExpressionVisitor
{
    protected override Expression VisitMethodCall(MethodCallExpression node)
    {
        if (node.Method.Name == "Where" && node.Method.DeclaringType == typeof(Queryable))
            return node.Arguments[0];
        else
            return base.VisitMethodCall(node);
    }
}

and:

public static class IQueryableExtensions
{
    public static IQueryable<T> RemoveWhere<T>(this IQueryable<T> expression)
    {
        var delExpr = Expression.Lambda<Func<IQueryable<T>>>(new WhereRemoveVisitor().Visit(expression.Expression)).Compile();
        return delExpr();
    }
}

Upvotes: 3

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