Beachwalker Beachwalker - 1 month ago 12
C# Question

Assign value to Nullable<T> using FastMember

I have successfully assigned values to Properties and nested Properties using this function

private static void AssignValueToProperty(ObjectAccessor accessor, object value, string propertyLambdaString)
{
var index = propertyLambdaString.IndexOf('.');

if (index == -1)
{
accessor[propertyLambdaString] = value;
// problem above: throws Exception if assigning value to Nullable<T>
}
else
{
var property = propertyLambdaString.Substring(0, index);
accessor = ObjectAccessor.Create(accessor[property]);

AssignValueToProperty(accessor, value, propertyLambdaString.Substring(index + 1));
}
}


However, the assignment throws an InvalidCastException. How to assign nullable values instead using FastMember? For example

public class A
{
public double? SomeValue {get; set;}
}

...
var a = new A();
var accessor = ObjectAccessor.Create(a);
accessor["SomeValue"] = 100; // throws Exception, when assigning 100.0 it works???

Answer

FastMember has nothing related to type conversion within it's toolbox, so this is the solution I came up with as Extension Method for FastMember ObjectAccessor:

public static class FastMemberExtensions
{
    public static void AssignValueToProperty(this ObjectAccessor accessor, string propertyName, object value)
    {
        var index = propertyName.IndexOf('.');

        if (index == -1)
        {
            var targetType = Expression.Parameter(accessor.Target.GetType());
            var property = Expression.Property(targetType, propertyName);

            var type = property.Type;
            type = Nullable.GetUnderlyingType(type) ?? type;
            value = value == null ? GetDefault(type) : Convert.ChangeType(value, type);
            accessor[propertyName] = value;
        }
        else
        {
            accessor = ObjectAccessor.Create(accessor[propertyName.Substring(0, index)]);
            AssignValueToProperty(accessor, propertyName.Substring(index + 1), value);
        }
    }

    private static object GetDefault(Type type)
    {
        return type.IsValueType ? Activator.CreateInstance(type) : null;
    }
}

Can be called this way:

var accessor = ObjectAccessor.Create(t); // t is instance of SomeType
accessor.AssignValueToProperty("Nested.Property", value); // t.Nested.Property = value
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