In our role-playing game example, we add a bunch of skills, that will be available to all characters. using the Fluent API; conventions will never setup a composite key, Creating Composite Key Entity Framework. Create the C# Console project as specified in this Entity Framework Code First tutorial. You must configure it using Fluent API. Viewed 92k times 58. The Entity Framework Core Fluent API HasForeignKey method is used to specify which property is the foreign key in a relationship. Data annotations and the fluent API can be used together, but Code First gives precedence to Fluent API > data annotations > default conventions. Fluent API is an advanced way of specifying model configuration that covers everything that data annotations can do in addition to some more advanced configuration not possible with data annotations. Define the key for this EntityType. You can configure the name of the alternate key's index and unique constraint: how to specify explicit values for generated properties. Copy link cilerler commented May 10, 2019. Owned entity types use different rules to define keys. You specify the properties that form the composite key by passing them in as properties of an anonymous type to the HasKey method. A key serves as a unique identifier for each entity instance. Code First Entity Framework 6: 1 to 1 with composite key. When there are composite keys in database table and when you try to put data annotation it will throw below error Entity type ‘Orgmember’ has composite primary key defined with data annotations. Composite keys can only be configured using the Fluent API; conventions will never setup a composite key, and you can not use Data Annotations to configure one. Entities can have additional keys beyond the primary key (see Alternate Keys for more information). In the following example, the AuthorFK property in the Book entity does not follow Entity Framework Core's convention for foreign key names. Active 6 years, 9 months ago. Composite keys can only be configured using the Fluent API; conventions will never setup a composite key, and you can not use Data Annotations to configure one. You have to use the fluent API to set up a composite key. You can also configure a single property to be an alternate key: You can also configure multiple properties to be an alternate key (known as a composite alternate key): Finally, by convention, the index and constraint that are introduced for an alternate key will be named AK__ (for composite alternate keys becomes an underscore separated list of property names). Composite Keys can only be created using the Fluent API, attributes just don’t know what to do when multiple [Key] fields are found. If a key property has its value generated by the database and a non-default value is specified when an entity is added, then EF will assume that the entity already exists in the database and will try to update it instead of inserting a new one. protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity() .HasKey(c => new { c.State, c.LicensePlate }); } Primary key name. Follow. Defining Columns, Primary, and Composite Keys in Entity Framework. With Fluent API we can override these configurations and explicitly defined the configuration that we want to set in the tables in the database. In EF Core, defining composite PK using KeyAttribute is not supported, therefore you must use fluent API to configure composite PK. If you just want to enforce uniqueness on a column, define a unique index rather than an alternate key (see Indexes). EF Core follows conventions to generate the database and the tables. Ask Question Asked 7 years, 4 months ago. You can configure a single property to be the primary key of an entity as follows: You can also configure multiple properties to be the key of an entity - this is known as a composite key. After SaveChanges is called the temporary value will be replaced by the value generated by the database. Composite keys can only be configured using the Fluent API - conventions will never setup a composite key and you can not use Data Annotations to configure one. In EF-core (current version 2.2.1) composite primary keys can't be modeled by data annotations. And so using data annotaion this is the metadata that is generated: However, if using fluent API instead of data annotation, the key part is not being generated at all. Let’s add an additional property to the Student class, just for the example sake: public Guid AnotherKeyProperty { get; set; } Now, we can configure the composite key: System.Data.Entity.Edm.EdmEntitySet: EntityType: EntitySet 'CustomerImages' is based on type 'CustomerImage' that has no keys defined. When using a relational database this maps to the concept of a unique index/constraint on the alternate key column(s) and one or more foreign key constraints that reference the column(s). So, in general, even a knight could throw a fireball and a mage can smash his opponent in a frenzy. Fluent API. Using Fluent API, you can change the corresponding column name, type, size, Null or NotNull, PrimaryKey, ForeignKey, concurrency column, etc. Attributes and Fluent API. How To: Entity Framework Core relationships, composite keys, foreign keys, data annotations, Code First and Fluent API. Left as it is, Entity Framework Core will create an AuthorFK field and an AuthorId field which it will configure as a foreign key: Composite keys are not covered by conventions or data annotation attributes. By using the .HasKey() method, a set of properties can be explicitly configured as the composite primary key of the entity. The Fluent API on the other hand is a bit more complex to use, but provides a far more advanced set of features. Fluent APIs are indicated prefxed by the “.”-character. And it will still generate Fluent API so EF Core is also happy. An alternate key serves as an alternate unique identifier for each entity instance in addition to the primary key; it can be used as the target of a relationship. The composite key is the same as above. In addition, you could also use Fluent API to achieve it, like this: modelBuilder.Entity().HasKey(t => new { t.Id, t.ProjectId }); For more information about composite primary key with Fluent API, please refer to: The only way we can create it using the HasKey method. The Fluent API can be used to configure properties of an entity to map it with a db column. As it turned out, I simply forgot putting the map on the DbContext: That said, the composite Id still not being populated on the $metadata this way. In some cases the key values can be converted to a supported type automatically, otherwise the conversion should be specified manually. Below an overview of the attributes and Fluent APIs that can be used in EF Core to configure its behavior. For more information see Keys in docs. Example. Vladimir Enchev. The following samples are designed to show how to do various tasks with the fluent api and allow you to copy the code out and customize it to suit your model, if you wish to see the model that they can be used with as-is then it is provided at the end of this article. But I keep getting the following exception: One or more validation errors were detected during model generation: There’s just a pool of skills that every character can choose from. By convention, an alternate key is introduced for you when you identify a property which isn't the primary key as the target of a relationship. You can configure the name of the primary key constraint as follows: While EF Core supports using properties of any primitive type as the primary key, including string, Guid, byte[] and others, not all databases support all types as keys. 9. 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