public static Expression <T> Compose <T>(this Expression <T> first, Expression <T> second, Func <Expression, Expression, Expression> merge)
{
var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);
var secondBody = ExpressionParameterRebinder.ReplaceParameters(map, second.Body);
return(Expression.Lambda <T>(merge(first.Body, secondBody), first.Parameters));
}
private Expression ReplaceExpressionParameters([NotNull] Expression cast,
[NotNull] Expression <Func <TCast, bool> > baseExpression)
{
// build parameter map (from parameters of second to parameters of first)
var map = baseExpression.Parameters.ToDictionary(p => p, p => cast);
// replace parameters in the second lambda expression with parameters from the first
var newBody = ExpressionParameterRebinder.ReplaceParameters(map, baseExpression.Body);
return(newBody);
}
protected override Expression BuildExpressionBody(Expression arg)
{
var matchExpression = _matchSpecification.GetExpression();
var expression =
ExpressionParameterRebinder.ReplaceParameters(new Dictionary <ParameterExpression, Expression>
{
{ matchExpression.Parameters.First(), arg }
},
matchExpression.Body);
return(expression);
}
private Expression <Func <T, bool> > ReplaceExpressionParameters(
[NotNull] Expression <Func <T, TProperty> > selector, [NotNull] Expression <Func <TProperty, bool> > expression)
{
// build parameter map (from parameters of second to parameters of first)
var map = expression.Parameters.ToDictionary(p => p, p => selector.Body);
// replace parameters in the second lambda expression with parameters from the first
var newBody = ExpressionParameterRebinder.ReplaceParameters(map, expression.Body);
// apply composition of lambda expression bodies to parameters from the first expression
return(Expression.Lambda <Func <T, bool> >(newBody, selector.Parameters));
}
protected override Expression BuildExpressionBody(Expression arg)
{
var fromExpression = _greaterThanSpecification.GetExpression();
var toExpression = _lessThanSpecification.GetExpression();
var fromExpressionBody = ExpressionParameterRebinder.ReplaceParameters(
new Dictionary<ParameterExpression, Expression>
{
{fromExpression.Parameters.First(), arg}
},
fromExpression.Body);
var toExpressionBody = ExpressionParameterRebinder.ReplaceParameters(
new Dictionary<ParameterExpression, Expression>
{
{toExpression.Parameters.First(), arg}
},
toExpression.Body);
var expression = Expression.AndAlso(fromExpressionBody, toExpressionBody);
return expression;
}
