/// <summary>
/// Rewrites the given expression to use the specified type as root.
/// </summary>
/// <param name="expression">
/// The expression.
/// </param>
/// <param name="delegateType">
/// The delegate type.
/// </param>
/// <param name="paramTypes">
/// The parameter types.
/// </param>
/// <returns>
/// The rewritten expression.
/// </returns>
/// <exception cref="ArgumentNullException">
/// <paramref name="expression" /> is null.
/// </exception>
/// <exception cref="ArgumentException">
/// <paramref name="expression" /> has zero or more than two parameters -or- <paramref name="expression" />
/// has two parameters but the second parameter is not a <see cref="WhereDelegate" />.
/// </exception>
protected virtual LambdaExpression GetLambdaExpression
(
LambdaExpression expression,
Type delegateType,
params Type[] paramTypes
)
{
if (expression == null)
{
throw new ArgumentNullException("expression");
}
int count = expression.Parameters.Count;
if (count != 1 && !(count == 2 && expression.Parameters.Last().Type == typeof(WhereDelegate)))
{
throw new ArgumentException
(
"expression must have 1 param, or 2 param if last is WhereDelegate.",
"expression"
);
}
var visitor = new ParameterReplaceVisitor(expression.Parameters[0], Expression.Parameter(_type, _alias));
Expression visited = visitor.Visit(expression.Body);
var parameters = new List <ParameterExpression>
{
Expression.Parameter(paramTypes[0], "x")
};
if (paramTypes.Length == 2)
{
var param = expression.Parameters[1];
var newParam = Expression.Parameter(param.Type, "where");
visitor = new ParameterReplaceVisitor(param, newParam);
visited = visitor.Visit(visited);
parameters.Add(newParam);
}
return(Expression.Lambda(delegateType, visited, parameters));
}
/// <summary>
/// Combines (merges) the provided expressions into one.
/// </summary>
/// <param name="expressions">
/// The expressions to merge.
/// </param>
/// <typeparam name="TSource">
/// The <see cref="System.Type" /> of the source entity.
/// </typeparam>
/// <typeparam name="TDestination">
/// The <see cref="System.Type" /> of the result.
/// </typeparam>
/// <returns>
/// The resulting expression.
/// </returns>
/// <exception cref="ArgumentNullException">
/// <paramref name="expressions" /> is null.
/// </exception>
/// <exception cref="ArgumentException">
/// If one or more of the provided expressions is neither of <see cref="MemberInitExpression" /> or
/// <see cref="NewExpression" />, or if any but the first expression is a <see cref="NewExpression" />.
/// </exception>
public static Expression <Func <TSource, TDestination> > Combine <TSource, TDestination>
(
params Expression <Func <TSource, TDestination> >[] expressions
)
{
if (expressions == null)
{
throw new ArgumentNullException("expressions");
}
bool allAreMemberInit = expressions
.Where(x => x != null)
.Skip(1) // skip first which may also be a NewExpression
.All(x => x.Body is MemberInitExpression);
if (!allAreMemberInit)
{
throw new ArgumentException
(
"All expressions must be MemberInitExpression except the first which can also be a NewExpression",
"expressions"
);
}
Expression first = expressions[0].Body;
NewExpression constructor;
var bindings = new List <MemberBinding>();
if (first.NodeType == ExpressionType.MemberInit)
{
var initializer = (MemberInitExpression)first;
constructor = initializer.NewExpression;
bindings.AddRange(initializer.Bindings.OfType <MemberAssignment>());
}
else if (first.NodeType == ExpressionType.New)
{
constructor = (NewExpression)first;
}
else
{
throw new ArgumentException
(
"The first expression is not a MemberInitExpression, nor is it a NewExpression",
"expressions"
);
}
ParameterExpression parameter = expressions[0].Parameters[0];
for (int i = 1; i < expressions.Length; i++)
{
if (expressions[i] == null)
{
continue;
}
var initializer = (MemberInitExpression)expressions[i].Body;
var replace = new ParameterReplaceVisitor(expressions[i].Parameters[0], parameter);
foreach (MemberAssignment binding in initializer.Bindings.OfType <MemberAssignment>())
{
Expression converted = replace.VisitAndConvert(binding.Expression, "Combine");
if (converted != null)
{
MemberAssignment assignment = Expression.Bind(binding.Member, converted);
bindings.Add(assignment);
}
}
}
MemberInitExpression combined = Expression.MemberInit(constructor, bindings);
return(Expression.Lambda <Func <TSource, TDestination> >(combined, parameter));
}