In most cases Entity Framework can infer which type is the dependent and which is the principal in a relationship. The following code configures the relationship to be required and then disables cascade delete. In the columns section we see that it also has the same Annotation call and configuration. The following examples use an incomplete class definition to illustrate these actions. Foreign Keys. Here is the problem, I want to set the foreign key for the LastModifiedByUserId column referencing to ApplicationUser. The Entity Framework Core Fluent API OnDelete method is used to specify the action which should take place on a dependent entity in a relationship when the principal is deleted.. The following code generates the CourseInstructor table with CourseID and InstructorID columns. This relationship is defined by creating a foreign key property on the database schema. The Entity Framework Core Fluent API HasForeignKey method is used to specify which property is the foreign key in a relationship. When working with Code First, you define your model by defining your domain CLR classes. As you can see in the above code that Key and ForeignKey attributes are used for ID property in StudentLogIn class, in order to mark it as Primary Key as well as Foreign Key. The default code first convention for ForeignKey relationship expects foreign key property name match with the … You can configure cascade delete on a relationship by using the WillCascadeOnDelete method. To configure a one-to-one relationship using Fluent API in EF Core, use the HasOne, WithOne and HasForeignKey methods, as shown below. In this article we will read about the Fluent API. Barebones introductory one, and then something more complex. It seemed easier to create a quick repo with a minimal example that demonstrates the issue than to inline all the code here. data-annotations. This page provides information about setting up relationships in your Code First model using the fluent API. As a result the CourseInstructor table is created with Course_CourseID and Instructor_InstructorID columns. Fluent Api, or Fluent Interface Pattern is a … These methods have overloads that do not take arguments and can be used to specify cardinality with unidirectional navigations. Next we have the Store table where we added the key with the Fluent API. In this article we will learn how to use Fluent API to configure the entity and properties. protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Entity() .HasRequired(b => b.Author) .WithMany(a => a.Books) .HasForeignKey< int >(b => b.AuthorId); } This is a good example of letting the conventions work for you! The HasRequired and HasOptional methods take a lambda expression that represents a reference navigation property. The Entity Framework Core Fluent API HasForeignKey method is used to specify which property is the foreign key in a relationship. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.\r\nCould not create constraint. A relationship, in the context of databases, is a situation that exists between two relational database tables when one table has a foreign key that references the primary key of the other table. When configuring a relationship with the fluent API, you start with the EntityTypeConfiguration instance and then use the HasRequired, HasOptional, or HasMany method to specify the type of relationship this entity participates in. Foreign Key You can use the HasForeignKey() method to configure the foreign key constraint name for a relationship. If you use the Code First naming conventions, in most cases you can rely on Code First to set up relationships between your tables based on the foreign keys and navigation properties that you define on the classes. We are going to see how w e can create relationships between classes using EF Core and Fluent API. The OnDelete method takes a DeleteBehavior enum as a parameter:. Step 3 – Next create DB Context class called CompanyContext.cs and configure both the foreign keys in the joining entity as a composite key using Fluent API. What is a Relationship? So by Adding the public int id { get; set; } we are able to trick … The EmployeeAddress class uses the EmployeeID as both Primary key & Foreign Key. The following example configures a one-to-zero-or-one relationship. By utilizing the Map method while establishing the Foreign Key relationship, any unique name can be used for Foreign Keys. To enable a foreign key to a non-existent model in you project, just use the fluent API to add or remove the constraint. This Series is about building C# Fullstack Web Applications in ASP.NET using MVC, Web API, the Entity Framework and a MS SQL Database. If a foreign key on the dependent entity is nullable, Code First does not set cascade delete on the relationship, and when the principal is deleted the foreign key will be set to null. You can then configure foreign key properties by using the HasForeignKey method. To make it a NotNull column, use the HasRequired() method as shown below. If you do not follow the conventions when defining your classes, or if you want to change the way the conventions work, you can use the fluent API or data annotations to configure your classes so Code First can map the relationships between your tables. When both ends of the relationship are required, use WithRequiredPrincipal or WithRequiredDependent after the HasRequired method. When the Equipment and Transaction entities are loaded into the working memory, EF knows to set the relevant dependent entities foreign keys to null. One to one relationships have a reference navigation property on both sides. Left as it is, Entity Framework Core will create an AuthorFK field and an AuthorId field which it will … In the following example, the default Code First conventions are used to create a join table. Cascade - dependents should be deleted; Restrict - dependents are unaffected; SetNull - the foreign key values in dependent rows should update to NULL It seems impossible to achieve your goal by Fluent API based on my knowledge, because the base class is abstract, the configuration doesn't work for 1 to many relation. But if we had a foreign key with a different name, StudId for example, then the HasForeignKey method would be needed because otherwise, EF core would create an optional relationship between Evaluation and Student classes. Foreign Key. If you want to specify the join table name and the names of the columns in the table you need to do additional configuration by using the Map method. The Convention requires us to have either Id property or EmployeeAddressID Property in the EmployeeAddress class. To configure Code First and the way it will generate our database, there are two methods: DataAnnotation and Fluent API. This enables us to basically run SQL queries on the target database. The HasMany method takes a lambda expression tha… The foreign key property will be discovered by convention if it is named [Target Type Key Name], [Target Type Name] + [Target Type Key Name], or [Navigation Property Name] + [Target Type Key Name]. By default, Entity Framework uses the Code First conventions to map your classes to the database schema. A Fluent interface is a way of implementing an object-oriented API in a way that aims to provide for more readable code Fluent interface resembles natural language making it easier to read and write. If a specific Foreign Key name is desired but is not contained as a property in the model, it can be set explicitly using the Fluent API. What is Fluent API. To configure one-to-zero or one relationship between Student and StudentLogIn using Fluent API, you need to override OnModelCreating method as shown in the following code. To illustrate this problem, let’s take a look at the following model: Configuring Relationships with The Fluent API. Shows configuring relationships in C# .NET code first entity framework using the Fluent API. Do this in the OnModelCreating() method. Cascade Delete in Fluent API for Foreign Keys EF Core behaves differently when the parent entity of the foreign key is deleted. Now let’s have a look at the third and final way which is defining the foreign key using Fluent API. So plan ahead. In convention 1, we have seen that it creates an optional one-to-many relationship which in turn creates a nullable foreign key column in the database. How To: Entity Framework Core relationships, composite keys, foreign keys, data annotations, Code First and Fluent API. Follow. You can remove these cascade delete conventions by using: modelBuilder.Conventions.Remove() In this example, a person or organization inherits from a party. This method takes a lambda expression that represents the property to be used as the foreign key. It is used to express the relationship between two tables. You can then configure an inverse navigation property by using the WithRequired, WithOptional, and WithMany methods. Fluent API approach for the One-to-Many Configuration. A relationship defines how two entities relate to each other. In “MyContext” class let's modify the OnModelCreating () method as follows and we are removing Data Annotations in the "Department" class. EF Code First has created a foreign key for us and it's great, but what we'd want is to use the ManagerId property. fluent-api. Configuring Foreign Keys With Fluent API BillingAddressId and DeliveryAddressId are foreign key scalar properties representing the actual foreign key values that the relationships are established on. If a foreign key on the dependent entity is not nullable, then Code First sets cascade delete on the relationship. For demonstration purpose, I’ve created a Console Application using .NET Core 3.1. Configure the NotNull ForeignKey using Fluent API. The following code configures a many-to-many relationship between the Course and Instructor types. The HasRequired and HasOptional methods take a lambda expression that represents a reference navigation property. Fluent API is implemented in DBModelbuilder class. Fluent API provides a full set of configuration options available in Code-First. In a relational database, this is represented by a foreign key constraint. A one-directional (also called unidirectional) relationship is when a navigation property is defined on only one of the relationship ends and not on both. Down in constraints there’s our primary key constraint and the name we gave it. protected override void OnModelCreating (DbModelBuilder modelBuilder) Each has a collection of addresses that can be associated with them. The DestinationIdproperty you added matched the first of these three rules. See this repository. When using the Fluent API, the ToTable method is used to control the table name and the owner within the OnModelCreating override in your class which derives from DbContext. If the primary key on the Department type consisted of DepartmentID and Name properties, you would configure the primary key for the Department and the foreign key on the Course types as follows: If you choose not to define a foreign key on the CLR type, but want to specify what name it should have in the database, do the following: If the foreign key property on the Course class was called SomeDepartmentID instead of DepartmentID, you would need to do the following to specify that you want SomeDepartmentID to be the foreign key: The following Code First model is used for the samples on this page. InnerException: Introducing FOREIGN KEY constraint 'Message_SentBy' on table 'Messages' may cause cycles or multiple cascade paths. modelBuilder.Conventions.Remove(). public class SchoolContext : DbContext { protected override void OnConfiguring ( DbContextOptionsBuilder optionsBuilder) { optionsBuilder.UseSqlServer ( "Server=.\\SQLEXPRESS;Database=EFCore-SchoolDB;Trusted_Connection=True" ); } protected override void OnModelCreating ( ModelBuilder modelBuilder) { modelBuilder… For example, if you want a one-to-one relationship between Instructor and OfficeAssignment, where you have a navigation property on only the Instructor type, you need to use the fluent API to configure this relationship. So let's modify our Project class to use this property vs. let Code First create it for us. The Fluent API HasForeignKey Method. The OfficeAssignment has the InstructorID property that is a primary key and a foreign key, because the name of the property does not follow the convention the HasKey method is used to configure the primary key. modelBuilder.Entity().HasKey(t => new { t.StudentId, t.TeacherId }); English (en) ... To set composite primary key, use fluent API. Then i tried using the fluent api in the model builder without the annotations. When configuring a relationship with the fluent API, you start with the EntityTypeConfiguration instance and then use the HasRequired, HasOptional, or HasMany method to specify the type of relationship this entity participates in. Entity Framework Fluent API uses the Fluent Interface. Sequence. Relationships allow relational databases to split and store data … © 2020 - Mike Brind.All rights reserved.Contact me at Outlook.com. This site uses cookies to analyse traffic, remember your preferences, and optimise your experience. By convention, Code First always interprets a unidirectional relationship as one-to-many. Index. However, when both ends of the relationship are required or both sides are optional Entity Framework cannot identify the dependent and principal. There's a breaking change between EF Core 2.1 and 2.2. When both ends of the relationship are optional, use WithOptionalPrincipal or WithOptionalDependent after the HasOptional method. Before we continue, let’s run Update-Database to actually create the database. For that reason, I’m about to make two of them. This is not possible in my case, since all my tables have a foreign key to it. However, the fluent api is forcing me to create the virtual property in the ApplicationUser entity. Using the Fluent API, we begin by declaring the navigation properties of the relationship. In the following example, the AuthorFK property in the Book entity does not follow Entity Framework Core's convention for foreign key names. For general information about relationships in EF and how to access and manipulate data using relationships, see Relationships & Navigation Properties. Vladimir Enchev. You can instruct EF Core to – delete the child row if the related parent row is … In the following example, the AuthorFK property in the Book entity does not follow Entity Framework Core's convention for foreign key names. The ForeignKey attribute is used to specify which property is the foreign key in a relationship. You can read about Fluent Interface from this link. Making fluent api isn’t complicated, but it can get messy quickly. You can configure this using Fluent API. Creating composite primary key consisting off foreign keys in fluent API with ASP.NET core c# entity-framework-core. The HasMany method takes a lambda expression that represents a collection navigation property. A side note before beggining. Your guide to using the latest version of Microsoft's Object Relational Mapper, Entity Framework Core's convention for foreign key names, Configuring Many To Many Relationships in Entity Framework Core, Executing Raw SQL Queries using Entity Framework Core, Generating a model from an existing database. Left as it is, Entity Framework Core will create an AuthorFK field and an AuthorId field which it will configure as a foreign key: The AuthorFK property is configured as the foreign key in the OnModelCreating method: The data annotations equivalent to the HasForeignKey method is the ForeignKey attribute. Fluent API provides more functionality for configuration than Data Annotations. Code configures the relationship Id property or EmployeeAddressID property in the EmployeeAddress class read about the API... First create it for us Entity and properties and properties Core 3.1 arguments and be. 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