ef how to insert a relationship student and course

So, when you add a Student in a Course or a Course in a Student entity and when you save it, it will then insert the PK of the added student and course in the StudentCourse table. So, this mapping not only enables a convenient association directly between the two entities, but also manages querying, inserts, and updates across these joins.

Full Answer

What is required to create a relationship in efef core?

EF Core will create a relationship if an entity contains a navigation property. Therefore, the minimum required for a relationship is the presence of a navigation property in the principal entity.

What is the relationship between studentID and studentaddress in Entity Framework?

Entity framework adds the Student reference navigation property into the StudentAddress entity and the StudentAddress navigation entity into the Student entity. Also, the StudentAddress entity has both StudentId property as PrimaryKey and ForeignKey, which makes it a one-to-one relationship.

How do I create a one-to-many relationship in EF?

In a one-to-many relationship, each table has a primary key that uniquely defines each row within the table. The easiest way to configure a one-to-many relationship is by convention. EF Core will create a relationship if an entity contains a navigation property.

How to understand the relationship in the Entity Framework Code first?

To understand the relationship in the Entity Framework Code First approach, we create an entity and define their configuration using the Fluent API. We will create two class library projects, one library project (EF.Core) has entities and another project (EF.Data) has these entities configuration with DbContext.

How do you create a relationship between two tables in Entity Framework?

In many-to-many relationship, a row in table A can have many matching rows in table B, and vice versa. You can create such a relationship by defining a third table, called a junction table, whose primary key consists of the foreign keys from both table A and table B.

What do you mean by many-to-many relationship between teacher and student entity?

Many-to-Many Relationship It means one Student can enroll for many Courses and also, one Course can be taught to many Students. The database includes the StudentCourse joining table which includes the primary key of both the tables ( Student and Course tables).

How do I create a one-to-many relationship in Entity Framework?

Configure One-to-Many RelationshipAdd Collection Navigation Property. You can achieve one-to-many relationship by adding the collection navigation property of Book entity in the Author entity class. ... Add Navigation Properties in Both Entities. ... Fully Defined Relationship.

How do you set up a many-to-many relationship?

To configure many-to-many relationship Using Data Annotations, you need to create the Join Table in the model.The Join Table BookCategory will have properties for the primary key of both the table.It will have two navigational properties one each for Book and Category class.More items...

What do you mean by one-to-many relationship between teacher and course table?

Answer: Explanation: In a "class roster" database, a teacher may teach zero or more classes, while a class is taught by one (and only one) teacher. This kind of relationship is known as one-to-many. ... The one-to-many relationship cannot be represented in a single table.

What do you mean by one-to-many relationship between class and student?

One student can have many classes. Many classes may have many student.

What is one-to-many relationship in database with example?

In a one-to-many relationship, one record in a table can be associated with one or more records in another table. For example, each customer can have many sales orders. In this example the primary key field in the Customers table, Customer ID, is designed to contain unique values.

What is ModelBuilder in Entity Framework?

Provides a simple API surface for configuring a IMutableModel that defines the shape of your entities, the relationships between them, and how they map to the database. You can use ModelBuilder to construct a model for a context by overriding OnModelCreating(ModelBuilder) on your derived context.

How do you create a foreign key relationship in code first approach?

To create Foreign Key, you need to use ForeignKey attribute with specifying the name of the property as parameter. You also need to specify the name of the table which is going to participate in relationship. I mean to say, define the foreign key table.

What is a one-to-many relationship?

In a relational database, a one-to-many relationship exists when one row in table A may be linked with many rows in table B, but one row in table B is linked to only one row in table A. It is important to note that a one-to-many relationship is not a property of the data, but rather of the relationship itself.

Where does the foreign key go in a 1 M relationship?

To map 1:m relationships, the primary key on the `one side' of the relationship is added to the `many side' as a foreign key.

Can a primary key be a foreign key?

Primary keys always need to be unique, foreign keys need to allow non-unique values if the table is a one-to-many relationship. It is perfectly fine to use a foreign key as the primary key if the table is connected by a one-to-one relationship, not a one-to-many relationship.

How are entities related in the Entity Framework?

In Entity Framework, an entity can be related to other entities through an association or relationship. Each relationship contains two ends that describe the entity type and the multiplicity of the type (one, zero-or-one, or many) for the two entities in that relationship.

How are relationships tracked?

Relationships are tracked through object references instead of foreign key properties. This type of association is called an independent association. The most common way to modify an independent association is to modify the navigation properties that are generated for each entity that participates in the association.

What is a foreign key association?

With foreign key properties included, you can create or change a relationship by modifying the foreign key value on a dependent object. This kind of association is called a foreign key association. Using foreign keys is even more essential when working with disconnected entities.

What are the different types of relationships?

There are generally three types of relationships: one-to-one, one-to-many, and many-to-many. In a one-to-many relationship, the foreign key is defined on the table that represents the many end of the relationship. The many-to-many relationship involves defining a third table (called a junction or join table), whose primary key is composed ...

What is a foreign key in relational databases?

In relational databases, relationships (also called associations) between tables are defined through foreign keys. A foreign key (FK) is a column or combination of columns that is used to establish and enforce a link between the data in two tables. There are generally three types of relationships: one-to-one, one-to-many, and many-to-many.

When you change the relationship of the objects attached to the context by using one of the methods described above, what does the

When you change the relationship of the objects attached to the context by using one of the methods described above, Entity Framework needs to keep foreign keys, references, and collections in sync. Entity Framework automatically manages this synchronization (also known as relationship fix-up) for the POCO entities with proxies. For more information, see Working with Proxies.

Does changing the relationship update the state of the dependent object?

In an independent relationship, changing the relationship does not update the state of the dependent object. The following examples show how to use the foreign key properties and navigation properties to associate the related objects.

What is the relationship between a student and a course?

The Student and Course have a Many-to-Many relationship marked by * multiplicity. It means one Student can enroll for many Courses and also, one Course can be taught to many Students. The database includes the StudentCourse joining table which includes the primary key of both the tables ( Student and Course tables).

How do teacher and standard have a relationship?

The Standard and Teacher entities have a One-to-Many relationship marked by multiplicity where 1 is for One and * is for Many. This means that Standard can have many Teachers whereas Teacher can associate with only one Standard .

What happens if foreign keys are not exposed on entity types in the conceptual model?

If foreign keys are not exposed on entity types in the conceptual model, deleting a navigation property may make the corresponding association traversable in only one direction or not traversable at all.

How to delete associations in EF Designer?

To delete an association. To delete an association do one of the following: Right-click the association on the EF Designer surface and select Delete. OR -. Select one or more associations and press the DELETE key.

Can you add foreign keys to entities?

It is recommended that you always expose foreign keys for relationships in your entities. In many-to-many (*:*) you cannot add foreign keys to the entities. In a *:* relationship, the association information is managed with an independent object.

Do you expose foreign keys in Entity Framework?

It is recommended that you always expose foreign keys for relationships in your entities. Entity Framework uses a referential constraint to identify that a property acts as the foreign key for a relationship.

What is the purpose of code first in Entity Framework?

By default, Entity Framework uses the Code First conventions to map your classes to the database schema. 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.

Can an entity framework identify the dependent and principal?

However, when both ends of the relationship are required or both sides are optional Entity Framework cannot identify the dependent and principal.

Is code first one to many?

By convention, Code First always interprets a unidirectional relationship as one-to-many. 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. C#.

What is a many to many relationship?

In a many-to-many relationship, each row of data in one table is linked to many rows in the second table and vice versa. For example, a book can appear in multiple categories and a category can contain many books.

What is a relational database?

Relationships. In relational databases, a relationship exists between two tables through foreign keys. A Foreign Key is a column or combination of columns that are used to establish and enforce a link between the data in those two tables. Entity framework Core supports three types of relationships;

What is the primary key in a book?

The primary key in Authors table is AuthorId, while in Books table the primary key is BookId. The AuthorId column in the Books table is a Foreign Key (FK), linking a book to its author. A book is a dependent entity in the relationship, and Author becomes the principal entity.

Can you have many to many relationships in EF Core?

In EF Core, many-to- many relationships are not yet supported without an entity class to represent the join table. You can represent a many-to-many relationship by including another entity class for the join table and mapping two separate one-to-many relationships.

Can you use foreign keys to link author row in database?

Using foreign keys, you can link one author row in the database to many book rows. Now if your model does not follow the default conventions, the Fluent API can be used to configure the correct relationship between entities. When configuring relationships with the Fluent API, you will use the Has/With pattern.

What is the many to many relationship between a student and a course?

There's a many-to-many relationship between the Student and Course entities, and the Enrollment entity functions as a many-to-many join table with payload in the database. This means that the Enrollment table contains additional data besides foreign keys for the joined tables (in this case, a primary key and a Grade property).

What is a one to zero relationship?

When there is a one-to-zero-or-one relationship or a one-to-one relationship between two entities (such as between OfficeAssignment and Instructor ), EF can't work out which end of the relationship is the principal and which end is dependent . One-to-one relationships have a reference navigation property in each class to the other class. The ForeignKey Attribute can be applied to the dependent class to establish the relationship. If you omit the ForeignKey Attribute, you get the following error when you try to create the migration:

What would happen if the enrollment table didn't include grade information?

If the Enrollment table didn't include grade information, it would only need to contain the two foreign keys CourseID and StudentID. In that case, it would correspond to a many-to-many join table without payload (or a pure join table) in the database, and you wouldn't have to create a model class for it at all.

What is required attribute?

The Required Attribute. The Required attribute makes the name properties required fields. The Required attribute is not needed for value types such as DateTime, int, double, and float. Value types cannot be assigned a null value, so they are inherently treated as required fields.

Why do we need foreign key in data model?

But having the foreign key in the data model can make updates simpler and more efficient. For example, when you fetch a course entity to edit, the Department entity is null if you don't load it, so when you update the course entity, you would have to first fetch the Department entity.

Is InstructorID nullable?

The Instructor entity has a nullable OfficeAssignment navigation property (because an instructor might not have an office assignment), and the OfficeAssignment entity has a non-nullable Instructor navigation property (because an office assignment can't exist without an instructor -- InstructorID is non-nullable). When an Instructor entity has a related OfficeAssignment entity, each entity will have a reference to the other one in its navigation property.

Can you use the fluent API for mapping?

In this tutorial you'll use the fluent API only for database mapping that you can't do with attributes. However, you can also use the fluent API to specify most of the formatting, validation, and mapping rules that you can do by using attributes.

Create Model

Add the following three classes in Program.cs file using the following code for Student class.

Create Database Context

The main class that coordinates Entity Framework functionality for a given data model is the database context class which allows to query and save data. You can create this class by deriving from the DbContext class and exposing a typed DbSet for each class in our model.

Database Initialization

In the above example, we have seen that Code First creates a database automatically, but if you want to change the name of the database and server, let us see how Code First decides the database name and server while initializing a database. Take a look at the following diagram.

No Parameter

If you specify the base constructor of the context class without any parameter as shown in the above example, then entity framework will create a database in your local SQLEXPRESS server with a name {Namespace}. {Context class name}.

Database Name

If you pass the database name as a parameter in a base constructor of the context class, then Code First will create a database automatically again, but this time the name will be the one passed as parameter in the base constructor on the local SQLEXPRESS database server.

Connection String Name

This is an easy way to tell DbContext to use a database server other than SQL Express or LocalDb. You may choose to put a connection string in your app.config file.

Domain Classes

So far we’ve just let EF discover the model using its default conventions, but there are going to be times when our classes don’t follow the conventions and we need to be able to perform further configuration. But you can override these conventions by configuring your domain classes to provide EF with the information it needs.

Relationships in EF

See more on docs.microsoft.com

Configuring Or Mapping Relationships

Creating and Modifying Relationships

Synchronizing The Changes Between The Foreign Keys and Navigation Properties

Loading Related Objects

Managing Concurrency

Working with Overlapping Keys

One-To-One Relationship

One-To-Many Relationship

Many-To-Many Relationship

• The Student and Course have a Many-to-Many relationship marked by * multiplicity. It means one Student can enroll for many Courses and also, one Coursecan be taught to many Students. The database includes the StudentCourse joining table which includes the primary key of both the tables(Student and Course tables). Entity Framework represents many-to...

See more on entityframeworktutorial.net

Associations Overview

Create and Delete Associations

Include Foreign Key Properties in Your Entities

• It is recommended that you always expose foreign keys for relationships in your entities. Entity Framework uses a referential constraint to identify that a property acts as the foreign key for a relationship. If you checked the Add foreign key properties to the <entity type name> Entitycheckbox when creating a relationship, this referential constra...

See more on docs.microsoft.com

Create and Edit Association Mappings

Edit and Delete Navigation Properties