public MappingTarget(MemberAccessPath memberSetter, MemberAccessPath memberGetter = null)
: base(memberSetter)
{
this.ValueSetter = memberSetter.Count > 1 ?
memberSetter.GetSetterExpWithNullInstancesInstantiation() :
memberSetter.GetSetterExp();
try
{
//build the getter from the getter member path if provided;
//try to figure out the getter from the setter member path otherwise
//(this will work if the member being accessed is a field or property
//but won't necessarily work for methods)
this.ValueGetter = memberGetter == null
? memberSetter.GetGetterExp()
: memberGetter.GetGetterExp();
}
catch (Exception)
{
//Must be provided from where to read the member.
//We don't always have the real need to 'read' the member being set (we need to write it).
//This could still be not a problem.
}
}
internal static LambdaExpression GetGetterExpWithNullChecks(this MemberAccessPath memberAccessPath)
{
if (memberAccessPath.Count == 0)
{
return(memberAccessPath.GetGetterExp());
}
if (memberAccessPath.Count == 1)
{
return(memberAccessPath.First().GetGetterExp());
}
var instanceType = memberAccessPath.EntryInstance;
var entryMember = memberAccessPath.First();
var returnType = memberAccessPath.Last().GetMemberType();
var entryInstance = Expression.Parameter(instanceType, "instance");
var labelTarget = Expression.Label(returnType, "label");
Expression accessPath = entryInstance;
var memberAccesses = new List <Expression>();
foreach (var memberAccess in memberAccessPath)
{
if (memberAccess is MethodInfo mi)
{
accessPath = Expression.Call(accessPath, mi);
}
else
{
if (memberAccess.DeclaringType != accessPath.Type)
{
accessPath = Expression.Convert(accessPath, memberAccess.DeclaringType);
}
accessPath = Expression.MakeMemberAccess(accessPath, memberAccess);
}
memberAccesses.Add(accessPath);
}
var nullConstant = Expression.Constant(null);
var returnNull = Expression.Return(labelTarget, Expression.Default(returnType));
var nullChecks = memberAccesses.Take(memberAccesses.Count - 1).Select(memberAccess =>
{
var equalsNull = Expression.Equal(memberAccess, nullConstant);
return((Expression)Expression.IfThen(equalsNull, returnNull));
}).ToList();
var exp = Expression.Block
(
nullChecks.Any() ? Expression.Block(nullChecks.ToArray())
: (Expression)Expression.Empty(),
Expression.Label(labelTarget, memberAccesses.Last())
);
var delegateType = typeof(Func <,>).MakeGenericType(instanceType, returnType);
return(LambdaExpression.Lambda(delegateType, exp, entryInstance));
}
