What is reference method in Entity Framework?
The Reference method should be used when an entity has a navigation property to another single entity. On the other hand, the Collection method should be used when an entity has a navigation property to a collection of other entities.
How do I use navigation property in Entity Framework?
A navigation property is an optional property on an entity type that allows for navigation from one end of an association to the other end. Unlike other properties, navigation properties do not carry data. A navigation property definition includes the following: A name.
How do you set a foreign key in EF?
The ForeignKey attribute is used to configure a foreign key in the relationship between two entities in EF 6 and EF Core. It overrides the default conventions. As per the default convention, EF makes a property as foreign key property when its name matches with the primary key property of a related entity.
What is OnModelCreating in Entity Framework?
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.
How do I add references to Entity Framework?
Go to references –> Add Reference –> in the dialog, choose COM and press browse. Then go to your project which is using EF and go to the projects bin folder where the EF references are stored. Select the EntityFramework. SqlServer.
What is proxies in Entity Framework?
Proxies. Proxies are objects deriving from your entities that are generated at runtime by Entity Framework Core. These proxies have behaviour added to them that result in database queries being made as required to load navigation properties on demand.
What are the types of property in Entity Framework?
An Entity can include two types of properties: Scalar Properties and Navigation Properties. Scalar Property: The type of primitive property is called scalar properties. Each scalar property maps to a column in the database table which stores the real data.
What are scalar and navigation properties in Entity Framework?
Basically a scalar property is mapped to a column (int, string.) A navigation property is mapped to a relation. e.g Order. OrderDetails brings you to all ORderDetails of a specific order.
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).
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.
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.
What is ModelBuilder in EF core?
The ModelBuilder is the class which is responsible for building the Model. The ModelBuilder builds the initial model from the entity classes that have DbSet Property in the context class, that we derive from the DbContext class. It then uses the conventions to create primary keys, Foreign keys, relationships etc.
How do you add a reference to a project?
You can also right-click the project node and select Add > Project Reference. If you see a References node in Solution Explorer, you can use the right-click context menu to choose Add Reference. Or, right-click the project node and select Add > Reference.
How do I add references to my console application?
Add a reference
- In Solution Explorer, right-click on the References or Dependencies node and choose either Add Project Reference, Add Shared Project Reference, or Add COM Reference.
- Specify the references to add, and then select OK.
Is lazy loading default in EF core?
Lazy Loading is the default behavior of LINQ that’s why it is the default behavior of EF Core. With lazy loading, all related entities are not loaded along with the parent entity automatically.
What is lazy loading in EF core?
Lazy loading means that the related data is transparently loaded from the database when the navigation property is accessed.
What is DbContext and DbSet in Entity Framework?
DbContext generally represents a database connection and a set of tables. DbSet is used to represent a table. Your code sample doesn’t fit the expected pattern.
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 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.
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 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.
Can foreign key be duplicate?
Short answer: Yes, it can be NULL or duplicate. I want to explain why a foreign key might need to be null or might need to be unique or not unique. First remember a Foreign key simply requires that the value in that field must exist first in a different table (the parent table). That is all an FK is by definition.
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.
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.
What is ModelBuilder in C#?
You can use ModelBuilder to construct a model for a context by overriding OnModelCreating(ModelBuilder) on your derived context. Alternatively you can create the model externally and set it on a DbContextOptions instance that is passed to the context constructor.