How to: Perform Safe Delete Without Foreign Key Constraints - Data Access - KB
Although the main purpose of a foreign key constraint is to control the no relationships between the tables in the database or that the foreign key constraints are not defined. In those cases it is possible to delete a parent entity leaving the What you need to do is to extend the domain context with a new. ''Cannot add foreign key constraint'' is a common MySQL error. Short Walks — Setting up a Foreign Key Relationship in Entity Framework [Snippet] .. data privacy and protection without sacrificing development efficiency. The ForeignKey attribute is used to configure a foreign key in the relationship between two entities in EF 6 and EF Core. It overrides the default conventions.
To this effect, entities will need to implement a property which reflects the state of the entity added, modified, deleted etc. Establishing some Scaffolding After generating the data model, the first thing to be done is ensure each entity derives from the same base class. As with my ongoing project, the Entity Framework DbContext is instantiated by this class on construction, and implements IDisposable to ensure the DbContext is disposed properly upon construction.
Updating a Many-to-Many Relationship Now things get interesting. This is mainly in case we need to reuse the logic, since it essentially processes state action on attached entities. Attach item ; if item.
DataAnnotations - ForeignKey Attribute in EF 7 & EF Core
Corresponding Unit Test The following unit test establishes the creation of a new many-to-many entity, it is then removed by relationship and then finally deleted altogether from the database: The one bug catch is that you need to specify the navigation property or collection, which might make it slightly undesirable to implement generically. Attach child ; obj. ChangeRelationshipState parent, child, expression, EntityState.
We need this level of access to get to the functionality which controls relationships. 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.
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.
CurrentGrade specifies that the Student entity has required the CurrentGrade property.
- 1) The Table or Index the Constraint Refers to Does Not Exist yet (Usual When Loading Dumps)
- Configure a One-to-Many Relationship using Fluent API