How do I add a foreign key in fluent API?
You can then configure foreign key properties by using the HasForeignKey method. This method takes a lambda expression that represents the property to be used as the foreign key.
What is fluent API used for?
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.
What is principal key in EF core?
Principal key: The properties that uniquely identify the principal entity. This may be the primary key or an alternate key. Foreign key: The properties in the dependent entity that are used to store the principal key values for the related entity.
What is OnModelCreating in Entity Framework Core?
The DbContext class has a method called OnModelCreating that takes an instance of ModelBuilder as a parameter. This method is called by the framework when your context is first created to build the model and its mappings in memory.
Is fluent API better than data annotation attributes?
The fluent API is considered a more advanced feature and we would recommend using Data Annotations unless your requirements require you to use the fluent API.
Can a primary key be a foreign key?
Yes, foreign key has to be primary key of parent table. Yes, it may not be unique and may have duplicate entries in child table, but it must be unique and does not have any duplicate entries at the parent table (as it is a primary key).
What is a DbContext?
A DbContext instance represents a combination of the Unit Of Work and Repository patterns such that it can be used to query from a database and group together changes that will then be written back to the store as a unit. DbContext is conceptually similar to ObjectContext.
Can foreign key be null?
A foreign key containing null values cannot match the values of a parent key, since a parent key by definition can have no null values. However, a null foreign key value is always valid, regardless of the value of any of its non-null parts.
What is HasKey in Entity Framework?
The Entity Framework Core Fluent API HasKey method is used to denote the property that uniquely identifies an entity (the EntityKey ), and which is mapped to the Primary Key field in a database: public class SampleContext : DbContext.
Is OnModelCreating required?
OnModelCreating is not necessary, but at the same time will not hurt if called – that’s why Sometimes it’s there, sometimes not. Sometimes at the beginning of the method, other times at the end.
Is required in fluent API?
The Entity Framework Core Fluent API includes two IsRequired methods. One is available on the PropertyBuilder type and is applied to a property to configure the mapped database column as not nullable.
What is EF core fluent API?
Entity Framework Fluent API is used to configure domain classes to override conventions. EF Fluent API is based on a Fluent API design pattern (a.k.a Fluent Interface) where the result is formulated by method chaining. In Entity Framework Core, the ModelBuilder class acts as a Fluent API.
Can a table have 2 primary keys?
Each table can only have one primary key. Access can automatically create a primary key field for you when you create a table, or you can specify the fields that you want to use as the primary key.
Can 2 tables have same primary key?
Every table can have (but does not have to have) a primary key. The column or columns defined as the primary key ensure uniqueness in the table; no two rows can have the same key. The primary key of one table may also help to identify records in other tables, and be part of the second table’s primary key.
Why do we use DbContext?
What is difference between DbContext and ObjectContext?
DbContext can be used for DataBase first, code first and model first development. DbContext mainly contains a set of APIs that are very easy to use. The API is exposed by ObjectContext.
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ObjectContext VS DBContext.
| ObjectContext | DbContext |
|---|---|
| ObjectContext supports self-tracking of Entities | DbContext does not support self-tracking of Entities. |
Can primary key be null?
A primary key defines the set of columns that uniquely identifies rows in a table. When you create a primary key constraint, none of the columns included in the primary key can have NULL constraints; that is, they must not permit NULL values.
Is Fluent API better than data annotation attributes?
What is data annotation in EF?
DataAnnotations is used to configure the classes which will highlight the most commonly needed configurations. DataAnnotations are also understood by a number of . NET applications, such as ASP.NET MVC which allows these applications to leverage the same annotations for client-side validations.
Where do you override OnModelCreating?
You can override the OnModelCreating method in your derived context and use the ModelBuilder API to configure your model. This is the most powerful method of configuration and allows configuration to be specified without modifying your entity classes.
What is ModelBuilder in MVC?
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.
Can primary key be NULL?
Can a unique key be NULL?
Key Differences Between Primary key and Unique key:
Primary key will not accept NULL values whereas Unique key can accept NULL values. A table can have only one primary key whereas there can be multiple unique key on a table.
Can we join tables without foreign key?
A foreign key is not required either. You can construct a query joining two tables on any column you wish as long as the datatypes either match or are converted to match.