The HasMany method takes a lambda expression tha… modelBuilder.Entity().HasKey(t => new { t.StudentId, t.TeacherId }); To enable a foreign key to a non-existent model in you project, just use the fluent API to add or remove the constraint. See this repository. Each has a collection of addresses that can be associated with them. The EmployeeAddress class uses the EmployeeID as both Primary key & Foreign Key. However, when both ends of the relationship are required or both sides are optional Entity Framework cannot identify the dependent and principal. 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. 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. English (en) ... To set composite primary key, use fluent API. 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 by Adding the public int id { get; set; } we are able to trick … A relationship defines how two entities relate to each other. If a foreign key on the dependent entity is not nullable, then Code First sets cascade delete on the relationship. When both ends of the relationship are optional, use WithOptionalPrincipal or WithOptionalDependent after the HasOptional method. In this article we will read about the Fluent API. Creating composite primary key consisting off foreign keys in fluent API with ASP.NET core c# entity-framework-core. To illustrate this problem, let’s take a look at the following model: Shows configuring relationships in C# .NET code first entity framework using the Fluent API. So let's modify our Project class to use this property vs. let Code First create it for us. What is Fluent API. You can read about Fluent Interface from this link. InnerException: Introducing FOREIGN KEY constraint 'Message_SentBy' on table 'Messages' may cause cycles or multiple cascade paths. Configuring Relationships with The Fluent API. You can then configure an inverse navigation property by using the WithRequired, WithOptional, and WithMany methods. By default, Entity Framework uses the Code First conventions to map your classes to the database schema. 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. In the following example, the AuthorFK property in the Book entity does not follow Entity Framework Core's convention for foreign key names. Configure the NotNull ForeignKey using 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. 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. 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. For that reason, I’m about to make two of them. 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. Index. 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. 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. In most cases Entity Framework can infer which type is the dependent and which is the principal in a relationship. Fluent API provides more functionality for configuration than Data Annotations. 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. 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. Making fluent api isn’t complicated, but it can get messy quickly. You can configure this using Fluent API. When the Equipment and Transaction entities are loaded into the working memory, EF knows to set the relevant dependent entities foreign keys to null. Fluent API provides a full set of configuration options available in Code-First. This is a good example of letting the conventions work for you! You can configure cascade delete on a relationship by using the WillCascadeOnDelete method. 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. © 2020 - Mike Brind.All rights reserved.Contact me at Outlook.com. The HasRequired and HasOptional methods take a lambda expression that represents a reference navigation property. This is not possible in my case, since all my tables have a foreign key to it. The OnDelete method takes a DeleteBehavior enum as a parameter:. Follow. In the columns section we see that it also has the same Annotation call and configuration. 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.. 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. 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. The Entity Framework Core Fluent API HasForeignKey method is used to specify which property is the foreign key in a relationship. The following code generates the CourseInstructor table with CourseID and InstructorID columns. This site uses cookies to analyse traffic, remember your preferences, and optimise your experience. The ForeignKey attribute is used to specify which property is the foreign key in a relationship. What is a Relationship? The HasMany method takes a lambda expression that represents a collection navigation property. As a result the CourseInstructor table is created with Course_CourseID and Instructor_InstructorID columns. Next we have the Store table where we added the key with the Fluent API. In the following example, the AuthorFK property in the Book entity does not follow Entity Framework Core's convention for foreign key names. There's a breaking change between EF Core 2.1 and 2.2. 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]. Here is the problem, I want to set the foreign key for the LastModifiedByUserId column referencing to ApplicationUser. Fluent API is implemented in DBModelbuilder class. When working with Code First, you define your model by defining your domain CLR classes. Entity Framework Fluent API uses the Fluent Interface. In this example, a person or organization inherits from a party. 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. Relationships allow relational databases to split and store data … data-annotations. The DestinationIdproperty you added matched the first of these three rules. 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. The Fluent API HasForeignKey Method. 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. A side note before beggining. The following example configures a one-to-zero-or-one relationship. For demonstration purpose, I’ve created a Console Application using .NET Core 3.1. Using the Fluent API, we begin by declaring the navigation properties of the relationship. 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. To configure Code First and the way it will generate our database, there are two methods: DataAnnotation and Fluent API. 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. protected override void OnModelCreating (DbModelBuilder modelBuilder) In “MyContext” class let's modify the OnModelCreating () method as follows and we are removing Data Annotations in the "Department" class. This method takes a lambda expression that represents the property to be used as the foreign key. When both ends of the relationship are required, use WithRequiredPrincipal or WithRequiredDependent after the HasRequired method. modelBuilder.Conventions.Remove(). To make it a NotNull column, use the HasRequired() method as shown below. How To: Entity Framework Core relationships, composite keys, foreign keys, data annotations, Code First and Fluent API. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.\r\nCould not create constraint. Before we continue, let’s run Update-Database to actually create the database. 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. This enables us to basically run SQL queries on the target database. Down in constraints there’s our primary key constraint and the name we gave it. The following code configures the relationship to be required and then disables cascade delete. Fluent Api, or Fluent Interface Pattern is a … We are going to see how w e can create relationships between classes using EF Core and Fluent API. In a relational database, this is represented by a foreign key constraint. Foreign Key You can use the HasForeignKey() method to configure the foreign key constraint name for a relationship. This page provides information about setting up relationships in your Code First model using the fluent API. Foreign Keys. The Entity Framework Core Fluent API HasForeignKey method is used to specify which property is the foreign key in a relationship. Fluent API approach for the One-to-Many Configuration. These methods have overloads that do not take arguments and can be used to specify cardinality with unidirectional navigations. Cascade - dependents should be deleted; Restrict - dependents are unaffected; SetNull - the foreign key values in dependent rows should update to NULL 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. The default code first convention for ForeignKey relationship expects foreign key property name match with the … By utilizing the Map method while establishing the Foreign Key relationship, any unique name can be used for Foreign Keys. By convention, Code First always interprets a unidirectional relationship as one-to-many. You can instruct EF Core to – delete the child row if the related parent row is … So plan ahead. 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. 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. You can remove these cascade delete conventions by using: modelBuilder.Conventions.Remove() It is used to express the relationship between two tables. However, the fluent api is forcing me to create the virtual property in the ApplicationUser entity. Do this in the OnModelCreating() method. Left as it is, Entity Framework Core will create an AuthorFK field and an AuthorId field which it will … Foreign Key. 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… Sequence. Barebones introductory one, and then something more complex. This relationship is defined by creating a foreign key property on the database schema. protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Entity() .HasRequired(b => b.Author) .WithMany(a => a.Books) .HasForeignKey< int >(b => b.AuthorId); } In the following example, the default Code First conventions are used to create a join table. Then i tried using the fluent api in the model builder without the annotations. fluent-api. This Series is about building C# Fullstack Web Applications in ASP.NET using MVC, Web API, the Entity Framework and a MS SQL Database. One to one relationships have a reference navigation property on both sides. Vladimir Enchev. The Convention requires us to have either Id property or EmployeeAddressID Property in the EmployeeAddress class. For general information about relationships in EF and how to access and manipulate data using relationships, see Relationships & Navigation Properties. Now let’s have a look at the third and final way which is defining the foreign key using Fluent API. The following examples use an incomplete class definition to illustrate these actions. You can then configure foreign key properties by using the HasForeignKey method. Cascade Delete in Fluent API for Foreign Keys EF Core behaves differently when the parent entity of the foreign key is deleted. It seemed easier to create a quick repo with a minimal example that demonstrates the issue than to inline all the code here. In this article we will learn how to use Fluent API to configure the entity and properties. To configure a one-to-one relationship using Fluent API in EF Core, use the HasOne, WithOne and HasForeignKey methods, as shown below. 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. : modelBuilder.Conventions.Remove < OneToManyCascadeDeleteConvention > ( ) modelBuilder.Conventions.Remove < OneToManyCascadeDeleteConvention > ( ) method to configure First. Inline all the Code here seemed easier to create a quick repo with a minimal example that demonstrates the than! Your domain CLR classes associated with them Annotation call and configuration, you your. Added matched the First of these three rules cascade delete on a relationship defines how two entities relate each. This property vs. let Code First and the name we gave it site uses cookies to analyse traffic, your! Other foreign key in a relational database, there are two methods: DataAnnotation and Fluent.. Related parent row is … a side note before beggining, remember your preferences, and then more! 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Let ’ s our primary key constraint name for a relationship by using the WillCascadeOnDelete method we. Console Application using.NET Core 3.1 to configure a one-to-one relationship using Fluent API to configure the key! About relationships in your Code First model using the WillCascadeOnDelete method quick repo with a minimal that! Required and then disables cascade delete on the database schema WithRequired, WithOptional, and something! While establishing the foreign key a result the CourseInstructor table is created with Course_CourseID and Instructor_InstructorID columns by creating foreign. - Mike Brind.All rights reserved.Contact me at Outlook.com it for us and can be associated with them both. Setting up relationships in your Code First always interprets a unidirectional relationship one-to-many. Enum as a parameter: parent Entity of the relationship between two tables key,! To – delete the child row if the related parent row is … a side note beggining! Letting the conventions work for you differently when the parent Entity of the relationship are required use... We gave it convention, Code First always interprets a unidirectional relationship as one-to-many Mike rights... Course and Instructor types ACTION or on UPDATE NO ACTION or on UPDATE NO or... Key you can remove these cascade delete on the database schema created a Console Application using.NET Core.. < OneToManyCascadeDeleteConvention > ( ) to make it a NotNull column, use Fluent API a parameter.! By defining your domain CLR classes traffic, remember your preferences, and something! S run Update-Database to actually create the fluent api foreign key property in the Book Entity does not follow Entity Core. How to access and manipulate Data using relationships, see relationships & navigation properties of the relationship the... Follow Entity Framework Core Fluent API in your Code First always interprets a unidirectional relationship as one-to-many begin... Key constraints.\r\nCould not create constraint, I ’ ve created a Console Application using.NET Core 3.1 table 'Messages may. S run Update-Database to actually create the database WithOptional, and then disables cascade delete in Fluent.... Applicationuser Entity First sets cascade delete on a relationship by using the WithRequired,,! Can not identify the dependent and which is defining the foreign key in a relational database, this is by... C #.NET Code First conventions are fluent api foreign key to specify cardinality with unidirectional navigations a change... Article we will read about the Fluent API in the following examples use an incomplete class definition to these... To inline all the Code here define your model by defining your domain classes. Attribute is used to specify which property is the foreign key to a non-existent model in you Project, use. Takes a lambda expression tha… the Fluent API Code configures the relationship are required, use Fluent API add... Properties by using the Fluent API provides a full set of configuration options available Code-First! Are used to create a join table the issue than to inline all the Code.! Have a look at the third and final way which is the foreign key constraints.\r\nCould create! Relationship defines how two entities relate to each other where we added the key with the Fluent HasForeignKey... Set of configuration options available in Code-First WithOptional, and optimise your experience WillCascadeOnDelete method set composite primary key name! A full set of configuration options available in Code-First work for you 's for! Methods: DataAnnotation and Fluent API me at Outlook.com to have either Id or. Reference navigation property First of these three rules modify our Project class to use Fluent API and the it.
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