private static NewExpression BuildNewExpression(ParameterExpression rootParameter, IReadOnlyDictionary <PropertyPath, ODataSelectColumnExpression> mapping)
{
// all paths longer than length 1 get grouped together and mapped to their own expression (this lets us support an arbitrary number of selected columns)
var nestedProperties = mapping.Where(kvp => kvp.Key.Count > 1).ToArray();
var nestedExpression = nestedProperties.Length > 0
? BuildNewExpression(rootParameter, nestedProperties.ToDictionary(kvp => kvp.Key.Skip(1).ToArray().As <PropertyPath>(), kvp => kvp.Value, PathComparer))
: Expression.Constant(false).As <Expression>();
// gather all argument expressions which will be used to initialize the type
var arguments = ProjectionTypeProperties.Take(ProjectionTypeProperties.Count - 1)
.Select(prop =>
{
ODataSelectColumnExpression selectColumn;
if (!mapping.TryGetValue(new[] { prop }, out selectColumn))
{
return(Expression.Constant(false));
}
var selectColumnPropertyPath = Traverse.Along(selectColumn.Expression, c => c.Expression)
.Select(m => m.Member)
.Reverse();
var expression = selectColumnPropertyPath.Aggregate(rootParameter.As <Expression>(), (acc, pi) => Expression.MakeMemberAccess(acc, pi));
return(expression);
})
.ToList();
arguments.Add(nestedExpression);
// build the new expression
var parameterizedType = ProjectionType.MakeGenericType(arguments.Select(a => a.Type).ToArray());
var newExpression = Expression.New(
parameterizedType.GetConstructors().Single(),
arguments,
members: parameterizedType.GetProperties(BindingFlags.Public | BindingFlags.Instance)
);
return(newExpression);
}
/// <summary>
/// Initializes a new assignment expression.
/// </summary>
/// <param name="left">The left operand of the assignment.</param>
/// <param name="right">The right operand of the assignment.</param>
/// <exception cref="ArgumentException"><paramref name="right"/> is not assignable to <paramref name="left"/>.</exception>
public NullCoalescingAssignmentExpression(ParameterExpression left, Expression right)
: this(left.As <Expression>(), right)
{
}