Create a Linq Expression with StartsWith, EndsWith and Contains passing a Expression<Func<T, string>>

Question

I want to create a method passing a expression of type Expression<Func<T, string> to create expression of type Expression<Func<T, bool>> to filter a string property with the StartsWith, EndsWith and Contains methods like these expressions:

.Where(e => e.MiProperty.ToUpper().StartsWith("ABC"));
.Where(e => e.MiProperty.ToUpper().EndsWith("XYZ"));
.Where(e => e.MiProperty.ToUpper().Contains("MNO"));

the method should look like:

public Expression<Func<T, bool>> AddFilterToStringProperty<T>(Expresssion<Func<T, string>> pMyExpression, string pFilter, FilterType pFiltertype)

where FilterType is an enum type that contains the three of the mentioned operations (StartsWith, EndsWith, Contains)

Answer 1

Try this:

public static Expression<Func<T, bool>> AddFilterToStringProperty<T>(
    Expression<Func<T, string>> expression, string filter, FilterType type)
{
    return Expression.Lambda<Func<T, bool>>(
        Expression.Call(
            expression.Body,
            type.ToString(),
            null,
            Expression.Constant(filter)),
        expression.Parameters);
}

Answer 2

Thanks @dtb. It works fine and I added a "not null" expression for this case like this:

public static Expression<Func<T, bool>> AddFilterToStringProperty2<T>(
                        Expression<Func<T, string>> expression, string filter, FilterType type)
    {
        var vNotNullExpresion = Expression.NotEqual(
                                expression.Body,
                                Expression.Constant(null));

        var vMethodExpresion = Expression.Call(
                expression.Body,
                type.ToString(),
                null,
                Expression.Constant(filter));

        var vFilterExpresion = Expression.AndAlso(vNotNullExpresion, vMethodExpresion);

        return Expression.Lambda<Func<T, bool>>(
            vFilterExpresion,
            expression.Parameters);
    }