I have two expressions of type Expression<Func<T, bool>> and I want to take to OR, AND or NOT of these and get a new expression of the same type
Expression<Func<T, bool>> expr1;
Expression<Func<T, bool>> expr2;
...
//how to do this (the code below will obviously not work)
Expression<Func<T, bool>> andExpression = expr AND expr2
Well, you can use Expression.AndAlso / OrElse etc to combine logical expressions, but the problem is the parameters; are you working with the same ParameterExpression in expr1 and expr2? If so, it is easier:
var body = Expression.AndAlso(expr1.Body, expr2.Body);
var lambda = Expression.Lambda<Func<T,bool>>(body, expr1.Parameters[0]);
This also works well to negate a single operation:
static Expression<Func<T, bool>> Not<T>(
this Expression<Func<T, bool>> expr)
{
return Expression.Lambda<Func<T, bool>>(
Expression.Not(expr.Body), expr.Parameters[0]);
}
Otherwise, depending on the LINQ provider, you might be able to combine them with Invoke:
// OrElse is very similar...
static Expression<Func<T, bool>> AndAlso<T>(
this Expression<Func<T, bool>> left,
Expression<Func<T, bool>> right)
{
var param = Expression.Parameter(typeof(T), "x");
var body = Expression.AndAlso(
Expression.Invoke(left, param),
Expression.Invoke(right, param)
);
var lambda = Expression.Lambda<Func<T, bool>>(body, param);
return lambda;
}
Somewhere, I have got some code that re-writes an expression-tree replacing nodes to remove the need for Invoke, but it is quite lengthy (and I can't remember where I left it...)
Generalized version that picks the simplest route:
static Expression<Func<T, bool>> AndAlso<T>(
this Expression<Func<T, bool>> expr1,
Expression<Func<T, bool>> expr2)
{
// need to detect whether they use the same
// parameter instance; if not, they need fixing
ParameterExpression param = expr1.Parameters[0];
if (ReferenceEquals(param, expr2.Parameters[0]))
{
// simple version
return Expression.Lambda<Func<T, bool>>(
Expression.AndAlso(expr1.Body, expr2.Body), param);
}
// otherwise, keep expr1 "as is" and invoke expr2
return Expression.Lambda<Func<T, bool>>(
Expression.AndAlso(
expr1.Body,
Expression.Invoke(expr2, param)), param);
}
Starting from .NET 4.0, there is the ExpressionVisitor class which allows you to build expressions that are EF safe.
public static Expression<Func<T, bool>> AndAlso<T>(
this Expression<Func<T, bool>> expr1,
Expression<Func<T, bool>> expr2)
{
var parameter = Expression.Parameter(typeof (T));
var leftVisitor = new ReplaceExpressionVisitor(expr1.Parameters[0], parameter);
var left = leftVisitor.Visit(expr1.Body);
var rightVisitor = new ReplaceExpressionVisitor(expr2.Parameters[0], parameter);
var right = rightVisitor.Visit(expr2.Body);
return Expression.Lambda<Func<T, bool>>(
Expression.AndAlso(left, right), parameter);
}
private class ReplaceExpressionVisitor
: ExpressionVisitor
{
private readonly Expression _oldValue;
private readonly Expression _newValue;
public ReplaceExpressionVisitor(Expression oldValue, Expression newValue)
{
_oldValue = oldValue;
_newValue = newValue;
}
public override Expression Visit(Expression node)
{
if (node == _oldValue)
return _newValue;
return base.Visit(node);
}
}
Nothing new here but married this answer with this answer and slightly refactored it so that even I understand what's going on:
public static class ExpressionExtensions
{
public static Expression<Func<T, bool>> AndAlso<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2)
{
ParameterExpression parameter1 = expr1.Parameters[0];
var visitor = new ReplaceParameterVisitor(expr2.Parameters[0], parameter1);
var body2WithParam1 = visitor.Visit(expr2.Body);
return Expression.Lambda<Func<T, bool>>(Expression.AndAlso(expr1.Body, body2WithParam1), parameter1);
}
private class ReplaceParameterVisitor : ExpressionVisitor
{
private ParameterExpression _oldParameter;
private ParameterExpression _newParameter;
public ReplaceParameterVisitor(ParameterExpression oldParameter, ParameterExpression newParameter)
{
_oldParameter = oldParameter;
_newParameter = newParameter;
}
protected override Expression VisitParameter(ParameterExpression node)
{
if (ReferenceEquals(node, _oldParameter))
return _newParameter;
return base.VisitParameter(node);
}
}
}
I combined some beautiful answers here to make it possible to easily support more Expression operators.
This is based on the answer of @Dejan but now it's quite easy to add the OR as well. I chose not to make the Combine function public, but you could do that to be even more flexible.
public static class ExpressionExtensions
{
public static Expression<Func<T, bool>> AndAlso<T>(this Expression<Func<T, bool>> leftExpression,
Expression<Func<T, bool>> rightExpression) =>
Combine(leftExpression, rightExpression, Expression.AndAlso);
public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> leftExpression,
Expression<Func<T, bool>> rightExpression) =>
Combine(leftExpression, rightExpression, Expression.Or);
public static Expression<Func<T, bool>> Combine<T>(Expression<Func<T, bool>> leftExpression, Expression<Func<T, bool>> rightExpression, Func<Expression, Expression, BinaryExpression> combineOperator)
{
var leftParameter = leftExpression.Parameters[0];
var rightParameter = rightExpression.Parameters[0];
var visitor = new ReplaceParameterVisitor(rightParameter, leftParameter);
var leftBody = leftExpression.Body;
var rightBody = visitor.Visit(rightExpression.Body);
return Expression.Lambda<Func<T, bool>>(combineOperator(leftBody, rightBody), leftParameter);
}
private class ReplaceParameterVisitor : ExpressionVisitor
{
private readonly ParameterExpression _oldParameter;
private readonly ParameterExpression _newParameter;
public ReplaceParameterVisitor(ParameterExpression oldParameter, ParameterExpression newParameter)
{
_oldParameter = oldParameter;
_newParameter = newParameter;
}
protected override Expression VisitParameter(ParameterExpression node)
{
return ReferenceEquals(node, _oldParameter) ? _newParameter : base.VisitParameter(node);
}
}
}
Usage is not changed and still like this:
Expression<Func<Result, bool>> noFilterExpression = item => filters == null;
Expression<Func<Result, bool>> laptopFilterExpression = item => item.x == ...
Expression<Func<Result, bool>> dateFilterExpression = item => item.y == ...
var combinedFilterExpression = noFilterExpression.Or(laptopFilterExpression.AndAlso(dateFilterExpression));
efQuery.Where(combinedFilterExpression);
(This is an example based on my actual code, but read it as pseudo-code)
I suggest one more improvement to PredicateBuilder and ExpressionVisitor solutions. I called it UnifyParametersByName and you can find it in MIT library of mine: LinqExprHelper. It allows for combining arbitary lambda expressions. Usually the questions are asked about predicate expression, but this idea extends to projection expressions as well.
The following code employs a method ExprAdres which creates a complicated parametrized expression, using inline lambda. This complicated expression is coded only once, and then reused, thanks to the LinqExprHelper mini-library.
public IQueryable<UbezpExt> UbezpFull
{
get
{
System.Linq.Expressions.Expression<
Func<UBEZPIECZONY, UBEZP_ADRES, UBEZP_ADRES, UbezpExt>> expr =
(u, parAdrM, parAdrZ) => new UbezpExt
{
Ub = u,
AdrM = parAdrM,
AdrZ = parAdrZ,
};
// From here an expression builder ExprAdres is called.
var expr2 = expr
.ReplacePar("parAdrM", ExprAdres("M").Body)
.ReplacePar("parAdrZ", ExprAdres("Z").Body);
return UBEZPIECZONY.Select((Expression<Func<UBEZPIECZONY, UbezpExt>>)expr2);
}
}
And this is the subexpression building code:
public static Expression<Func<UBEZPIECZONY, UBEZP_ADRES>> ExprAdres(string sTyp)
{
return u => u.UBEZP_ADRES.Where(a => a.TYP_ADRESU == sTyp)
.OrderByDescending(a => a.DATAOD).FirstOrDefault();
}
What I tried to achieve was to perform parametrized queries without need to copy-paste and with ability to use inline lambdas, which are so pretty. Without all these helper-expression stuff, I would be forced to create whole query in one go.
using System;
using System.Linq.Expressions;
namespace Extensions
{
public class Example
{
//How to use it
public static void Main()
{
Expression<Func<string, bool>> expression1 = exp => true;
Expression<Func<string, bool>> expression2 = exp => false;
Expression<Func<string, bool>> expression3 = ExpressionExtensions.AndAlso(expression1, expression2);
Expression<Func<string, bool>> expression4 = ExpressionExtensions.OrElse(expression1, expression2);
Expression<Func<string, bool>> expression = ExpressionExtensions.AndAlso(expression3, expression4);
}
}
public static class ExpressionExtensions
{
public static Expression<Func<T, bool>> AndAlso<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2)
{
ParameterExpression parameter1 = expr1.Parameters[0];
var visitor = new ReplaceParameterVisitor(expr2.Parameters[0], parameter1);
var body2WithParam1 = visitor.Visit(expr2.Body);
return Expression.Lambda<Func<T, bool>>(Expression.AndAlso(expr1.Body, body2WithParam1), parameter1);
}
public static Expression<Func<T, bool>> OrElse<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2)
{
ParameterExpression parameter1 = expr1.Parameters[0];
var visitor = new ReplaceParameterVisitor(expr2.Parameters[0], parameter1);
var body2WithParam1 = visitor.Visit(expr2.Body);
return Expression.Lambda<Func<T, bool>>(Expression.OrElse(expr1.Body, body2WithParam1), parameter1);
}
private class ReplaceParameterVisitor : ExpressionVisitor
{
private readonly ParameterExpression _oldParameter;
private readonly ParameterExpression _newParameter;
public ReplaceParameterVisitor(ParameterExpression oldParameter, ParameterExpression newParameter)
{
_oldParameter = oldParameter;
_newParameter = newParameter;
}
protected override Expression VisitParameter(ParameterExpression node)
{
if (ReferenceEquals(node, _oldParameter))
return _newParameter;
return base.VisitParameter(node);
}
}
}
}