Generate lambda Expression By Clause using string.format in C#?

Question

I have a method to Generate Expression By Clause as below:

internal static Expression<Func<TModel, T>> GenExpressionByClause<TModel, T>(string column)
    {
        PropertyInfo columnPropInfo = typeof(TModel).GetProperty(column);

        var entityParam = Expression.Parameter(typeof(TModel), "e");                    // {e}
        var columnExpr = Expression.MakeMemberAccess(entityParam, columnPropInfo); // {e.column}
        var lambda = Expression.Lambda(columnExpr, entityParam) as Expression<Func<TModel, T>>; // {e => e.column}
        return lambda;

    }

So I could build lambda expression as e=>e.column. but I want to change it to e=>string.Format("{0}",e.column). How could I refactor the code?

Romain Verdier · Accepted Answer · 2010-03-09 10:23:34Z

3

This should do the work:

    internal static Expression<Func<TModel, T>> GenExpressionByClause<TModel, T>(string column)
    {
        var columnPropInfo = typeof(TModel).GetProperty(column);
        var formatMethod = typeof (string).GetMethod("Format", new[] {typeof (string), typeof (object)});

        var entityParam = Expression.Parameter(typeof(TModel), "e");
        var columnExpr = Expression.MakeMemberAccess(entityParam, columnPropInfo);
        var formatCall = Expression.Call( formatMethod, Expression.Constant("{0}"), columnExpr);
        var lambda = Expression.Lambda(formatCall , entityParam) as Expression<Func<TModel, T>>;
        return lambda;
    }

Note that you could cache the Format MethodInfo in a static field.

answered Mar 9, 2010 at 10:23

Romain Verdier

13.1k7 gold badges60 silver badges77 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Sam Zhou · Accepted Answer · 2010-03-10 06:18:21Z

0

Final solution:

internal static Expression<Func<TModel, string>> GenExpressionByClauseEx<TModel>(string column)
    {
        var columnPropInfo = typeof(TModel).GetProperty(column);
        var formatMethod = typeof(String).GetMethod("Format", new[] { typeof(string), typeof(Object) });
        //string.Format(
        var entityParam = Expression.Parameter(typeof(TModel), "e");
        var columnExpr = Expression.MakeMemberAccess(entityParam, columnPropInfo);
        var columnExprObj=Expression.Convert(columnExpr, typeof(object));
        var formatCall = Expression.Call(formatMethod, Expression.Constant("111--{0}"), columnExprObj);
        var lambda = Expression.Lambda(formatCall, entityParam) as Expression<Func<TModel, string>>;
        return lambda;

    }

answered Mar 10, 2010 at 6:18

Sam Zhou

7152 gold badges7 silver badges9 bronze badges

1 Comment

Sky Sanders Over a year ago

@Sam - your final resolution would be better placed as an update to your original question.

Collectives™ on Stack Overflow

Generate lambda Expression By Clause using string.format in C#?

2 Answers 2

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related