CODEWITHSUNDEEP
c#linq
Artyomska
Artyomska

Reputation: 1335

Convert expression tree from equal to contains

In my server I currently have a method that checks if the field of an object equals a given string, and it looks like this:

var parameter = Expression.Parameter(typeof(Book), "b");
var predicate = Expression.Lambda<Func<Book, bool>>(Expression.Equal(Expression.PropertyOrField(parameter, filterAfter), Expression.Constant(filterField)),parameter);

To exemplify, if filterAfter is "title" and filterField is "Castle", then the expression will do book.title == "Castle". What I want to do is to convert the expression above to check if book.title contains the substring "Castle" in the title. How can I achieve that?

Upvotes: 2

Views: 296

Answers (1)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726709

Use Expression.Call

var containsMethod = typeof(string).GetMethod(nameof(string.Contains), new[] {typeof(string)});
var predicate = Expression.Lambda<Func<Book, bool>>(
    Expression.Call(
        Expression.PropertyOrField(parameter, filterAfter)
    ,   containsMethod
    ,   new Expression[] { Expression.Constant(filterField) }
    )
,   parameter
);

Upvotes: 1

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