Intro<\/h5>\n\n\n\n
Let's start by installing the following ef core packages.<\/p>\n\n\n\n
Install-Package Microsoft.EntityFrameworkCore<\/strong><\/p>\n\n\n\n Install-Package Microsoft.EntityFrameworkCore.Tools<\/strong><\/p>\n\n\n\n Firstly, We define two entity called Post <\/strong>and Tag <\/strong>. Every post could has more than one Tag, every tag could has more than one Post.<\/p>\n\n\n\n Post.cs<\/strong><\/p>\n\n\n\n Tag.cs<\/strong><\/p>\n\n\n\n In this state, first migration will create then ef core will create table called PostTag <\/strong> automatically but we cant access as class to this table.<\/p>\n\n\n\n Alternatively We can define the relationship using fluent api.<\/p>\n\n\n\n The difference of the method below between above is that we create the indermate table, so we can check on table.<\/p>\n\n\n\n PostTag.cs<\/strong><\/p>\n\n\n\n Post.cs<\/strong><\/p>\n\n\n\n Tag.cs<\/strong><\/p>\n\n\n\n Create<\/strong><\/p>\n\n\n\n Add to Exist Record<\/strong><\/p>\n\n\n\n Update<\/strong><\/p>\n\n\n\n At Many to Many<\/strong> relationships could has more than one update cases. For example we update post entity and the payload are content, title etc. tags are string array. In this case, we could happen this cases:<\/p>\n\n\n\n The three case can be at same time therefore all cases can be done in single code block. Firstly we're remove all tags of the entity to be updated. Then we add it if exist in tags table, otherwise we create a new tag.<\/p>\n\n\n\n Delete<\/strong><\/p>\n\n\n\n We could remove the tags of post without any restrictions thus if we remove one record in tags table, removed from all posts associated with that tag. This operation is CascadeDelete<\/strong>.<\/p>\n\n\n\n G\u00f6nderinin sonuna geldik, okudu\u011funuz i\u00e7in te\u015fekk\u00fcrler \ud83d\ude42 ba\u015fka bir g\u00f6nderide g\u00f6r\u00fc\u015fmek \u00fczere.<\/p>","protected":false},"excerpt":{"rendered":" In this post, we going to look how to use many to many relationship at entityframewok core 6.0.<\/p>","protected":false},"author":1,"featured_media":791,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[91,87,17,42],"tags":[108,45,105,109],"yoast_head":"\nFirst Solution<\/h5>\n\n\n\n
public class Post\n{\n public int Id { get; set; }\n public string Title { get; set; } = string.Empty;\n public string Content { get; set; } = string.Empty;\n\n public virtual ICollection<Tag>? Tags { get; set; }\n}<\/pre><\/div>\n\n\n\npublic class Tag\n{\n public int Id { get; set; }\n public string Name { get; set; } = string.Empty;\n\n public virtual ICollection<Post>? Posts { get; set; }\n}<\/pre><\/div>\n\n\n\n![\"\"](\"https:\/\/okankaradag.com\/wp-content\/uploads\/2022\/09\/manytomany.png\")
<\/figure>\n\n\n\nCommon table as manuel and FluentApi usage<\/strong> (Second Solution)<\/h5>\n\n\n\n
public class PostTag\n{\n public int PostId { get; set; }\n public int TagId { get; set; }\n\n public virtual Post Post { get; set; }\n public virtual Tag Tag { get; set; }\n}<\/pre><\/div>\n\n\n\npublic class Post\n{\n public int Id { get; set; }\n public string Title { get; set; } = string.Empty;\n public string Content { get; set; } = string.Empty;\n\n public virtual ICollection<PostTag> PostTags { get; set; }\n\n}<\/pre><\/div>\n\n\n\npublic class Tag\n{\n public int Id { get; set; }\n public string Name { get; set; } = string.Empty;\n\n public virtual ICollection<PostTag> PostTags { get; set; }\n}<\/pre><\/div>\n\n\n\nFluentApi<\/strong><\/h5>\n\n\n\n
modelBuilder.Entity<PostTag>()\n .HasKey(pt => new { pt.PostId, pt.TagId });\n modelBuilder.Entity<PostTag>().HasOne(pt => pt.Post)\n .WithMany(p => p.PostTags)\n .HasForeignKey(pt => pt.PostId);\n modelBuilder.Entity<PostTag>().HasOne(pt => pt.Tag)\n .WithMany(p => p.PostTags)\n .HasForeignKey(pt => pt.TagId);<\/pre><\/div>\n\n\n\nCrud operations (Create - Update - Delete)<\/h5>\n\n\n\n
var post = new Post\n{\n Content = \"Post Content\",\n Title = \"Post Title\",\n Tags = new List<Tag>\n {\n new Tag\n {\n Name = \"Tag 1\"\n },\n new Tag\n {\n Name = \"Tag 2\"\n }\n }\n};\ndbContext.Posts.Add(post);\ndbContext.SaveChanges();<\/pre><\/div>\n\n\n\nvar tagIds = new int[] { 1, 2 }; \/\/exist tags\nvar tags = dbContext.Tags.Where(t => tagIds.Contains(t.Id)).ToList();\n \nvar post = new Post\n{\n Content = \"Post Content 2\",\n Title = \"Post Title 2\",\n Tags = tags\n};\n\ndbContext.Posts.Add(post);\ndbContext.SaveChanges();<\/pre><\/div>\n\n\n\nvar newTags = new string[] { \"Tag 1\", \"Tag 2\", \"Tag 3\" };\nvar post = dbContext.Posts.Include(p => p.Tags).FirstOrDefault();\nArgumentNullException.ThrowIfNull(post);\npost.Tags.Clear();\nforeach (var item in newTags)\n{\n var existItem = dbContext.Tags.FirstOrDefault(x => x.Name == item);\n if (existItem == null)\n {\n var tag = new Tag { Name = item };\n post.Tags.Add(tag);\n continue;\n }\n post.Tags.Add(existItem);\n }\n dbContext.SaveChanges();\n}<\/pre><\/div>\n\n\n\nvar tag = dbContext.Tags.FirstOrDefault(x => x.Name == \"Tag 1\");\nArgumentNullException.ThrowIfNull(tag);\ndbContext.Tags.Remove(tag);\ndbContext.SaveChanges();<\/pre><\/div>\n\n\n\n