c# - How delete many-to-many relation in Entity Framework 6 - Stack Overflow
middle` (`ID`) ON DELETE NO ACTION ON UPDATE NO ACTION); So I changed "middles" navigation property on "left" from "* (Many)" to "1. Learn what is cascading delete in EF 6 code-first approach and how to turn it off. types of relationships such as one-to-one, one-to-many and many-to-many. EF Core implements several different delete behaviors and allows for the (A non-nullable foreign key is equivalent to a required relationship.) In EF Core, unlike EF6, cascading effects do not happen immediately, but.
WriteLine " Saving changes: Cascade with required or optional relationship After loading entities: Blog '1' is in state Unchanged with 2 posts referenced. Post '1' is in state Unchanged with FK '1' and reference to blog '1'.Entity Framework - Insert Update and Delete in C#
Post '2' is in state Unchanged with FK '1' and reference to blog '1'. After deleting blog '1': Blog '1' is in state Deleted with 2 posts referenced.
- Solving the Detached Many-to-Many Problem with the Entity Framework
- Cascade Delete
- Configure One-to-Many Relationships in EF 6
Blog '1' is in state Detached with 2 posts referenced. Post '1' is in state Detached with FK '1' and no reference to a blog. Post '2' is in state Detached with FK '1' and no reference to a blog. SetNull with required relationship After loading entities: Posts'; column does not allow nulls. The statement has been terminated.
Configure One-to-Many Relationship in Entity Framework 6
SetNull with optional relationship After loading entities: Post '1' is in state Unchanged with FK 'null' and no reference to a blog. Post '2' is in state Unchanged with FK 'null' and no reference to a blog. Restrict with required or optional relationship After loading entities: The association between entity types 'Blog' and 'Post' has been severed but the foreign key for this relationship cannot be set to null.
If the dependent entity should be deleted, then setup the relationship to use cascade deletes. Blog is marked as Deleted Posts initially remain Unchanged since cascades do not happen until SaveChanges Since Restrict tells EF to not automatically set the FK to null, it remains non-null and SaveChanges throws without saving Delete orphans examples The code below is part of a sample that can be downloaded and run.
Clear ; DumpEntities " After making posts orphans: After making posts orphans: Post '1' is in state Modified with FK '1' and no reference to a blog.
Cascade Delete - EF Core | Microsoft Docs
You don't need to configure anything else. Let's look at an example of all the conventions which create a one-to-many relationship.
Convention 1 We want to establish a one-to-many relationship between the Student and Grade entities where many students are associated with one Grade. It means that each Student entity points to a Grade. This can be achieved by including a reference navigation property of type Grade in the Student entity class, as shown below.
Many-to-many relationships in EF Core 2.0 – Part 1: The basics
So, there can be many students in a single grade. Convention 2 Another convention is to include a collection navigation property in the principal entity as shown below.
This also results in a one-to-many relationship between the Student and Grade entities. This example produces the same result in the database as convention 1.
Convention 3 Including navigation properties at both ends will also result in a one-to-many relationship, as shown below. Convention 4 A fully defined relationship at both ends will create a one-to-many relationship, as shown below. This will create a one-to-many relationship with the NotNull foreign key column in the Students table, as shown below.
If the data type of GradeId is nullable integer, then it will create a null foreign key. However, you may configure relationships using Fluent API at one place to make it more maintainable.
Consider the following Student and Grade entity classes. First, we need to start configuring with any one entity class.