Convert to Nullable Decimal in Expression Trees

Question

My models have Nullable decimal types. So in my Expression trees it gave me the following error:

The binary operator Equal is not defined for the types 'System.Nullable`1[System.Decimal]' and 'System.Decimal'

Now I want to convert a string to decimal? and for that matter I have tried as:

decimal? res = Convert.ToDecimal(mystr); // this gives me type as System.Decimal

I have also looked to the answers of this, this, this and this. They all convert it into type System.Decimal and my expression trees gave the error mentioned above.

I really need to convert them to System.Nullable(System.Decimal) to work for me.

How can I work it out? My models are generated from Entity Framework EDMX so I cannot change their types. I have to do the conversion in the code.

it isn't.. when i checked as var d = res.GetType(); it gave me System.Decimal. and Expression tree also gave the same error — Awais Mahmood, Feb 06 '16 at 08:17
@AwaisMahmood: No, the type of `res` is `decimal?`. However, when you call `GetType()` it's boxing that to `decimal`... that's the way boxing works with nullable value types. The expression tree problem is pretty different. — Jon Skeet, Feb 06 '16 at 08:25

score 4 · Accepted Answer · answered Feb 06 '16 at 08:17

The normal C# code example you've shown has converted to decimal?, using the implicit conversion from T to T? for any non-nullable value type T.

In an expression tree, you just need to use Expression.Convert to perform that conversion, e.g.

// Assuming beforeConversion is an expression tree with a type of
// decimal
var converted = Expression.Convert(beforeConversion, typeof(decimal?));

Convert to Nullable Decimal in Expression Trees

1 Answers1