EF Core 如何使用 linq 将字段存储匹配为字符串但包含由分隔符分隔的项目

Question

For example. This table, I want to search items taged with 'c', not with 'c#' or 'c++'. Tags are seperated by a space.

ID  |  BookName              |  Tags 

1   |  C++ Primer            | c++ 
2   | .NET Core 3.1 Tutorial | c# .net
3   | Beginner Tutorial      | c c# c++

Each book record can be marked with multiple tags, If I use

dbContext.Book.Where(a => a.Tags.Contains("c")).ToList()

I'll get all of them. But I only want get Beginner Tutorial . Since I can not use = to filter the Tag field. How can I solve this?

PS: I can not change the structure of this table, either.

Answer 1

You could Split the Tags Fields on delimiter (in your case whitespace) and verify if the tag is present. For example

var result = dbContext.Book.Where(a => a.Tags.Split(' ').Contains("c"));

Answer 2

You need to first Split Tags by whitespace then you can use Contains or Any

By doing this with Contains :

var result = dbContext.Book.Where(a => a.Tags.Split(' ').Contains("c"));

By doing this with Any :

var result = dbContext.Book.Where(a => a.Tags.Split(' ').Any(t => t.Equals("c")))

These will give you expected result.

You can also check difference-between-contains-and-any-in-linq

Answer 3

var result = dbContext.Book.Where(a => a.Tags.Split(' ').Any(t => t.Equals("c")))

Answer 4

You can do it by regex too.

Regex regex = new Regex(@"^c$| c|c ");
var result = books.Where(a => regex.Match(a.Tags).Success);

Answer 5

Modify your model as follows :

public string Tags
    {
        get
        {
            return TagsList != null
                ? String.Join(" ", TagsList.Select(tag => tag ))
                : null;
        }
        set
        {
            TagsList = !String.IsNullOrWhiteSpace(value)
                ? value.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).ToList()
                : new List<string>();
        }
    }

[NotMapped]
public List<string> TagsList { get; set; }

Then use :

dbContext.Books.Where(a=>a.TagsList.Contains("c"));