Fluent API in Entity Framework Core

Entity Framework Core Fluent API is used to build model based on entity classes. We can also override the default Conventions of Entity Framework Core using Fluent API when targetting the database schema as Fluent API has higher precedence than conventions and data annotations.

Entity Framework Core Fluent API offers the following features.

• Model Configuration: Configures an EF model to database mappings.
• Entity Configuration: Configures PrimaryKey, AlternateKey, Index, table name, one-to-one, one-to-many, many-to-many relationships etc.
• Property Configuration: Configures property to column mapping e.g. column name, default value, nullability, Foreignkey, data type, etc.

This tutorial is a part of Entity Framework Core series.

• 1. Introduction to Entity Framework Core
• 2. Installation of Entity Framework Core
• 3. Database-First approach in Entity Framework Core
• 4. DbContext Class in Entity Framework Core
• 5. Code-First Approach in Entity Framework Core
• 6. Migrations in Entity Framework Core
• 7. Insert Records in Entity Framework Core
• 8. Read Records in Entity Framework Core
• 9. Update Records in Entity Framework Core
• 10. Delete Records in Entity Framework Core
• 11. Conventions in Entity Framework Core
• 12. Configurations in Entity Framework Core
• 13. Fluent API in Entity Framework Core
• 14. Configure One-to-Many relationship using Fluent API in Entity Framework Core
• 15. Configure One-to-One relationship using Fluent API in Entity Framework Core
• 16. Configure Many-to-Many relationship using Fluent API in Entity Framework Core
• 17. Execute Raw SQL Queries using FromSqlRaw() method in Entity Framework Core
• 18. Execute SQL Stored Procedures using FromSqlRaw() & ExecuteSqlRawAsync() methods in Entity Framework Core

Entity Framework Core Fluent API Example

Suppose we have am entity class named Country as shown below.

public class Country
{
    public int PId { get; set; }
 
    public string Name { get; set; }
 
    public DateTime AddedOn { get; set; }
}

We write Entity Framework Core Fluent API Configurations inside the OnModelCreating() method of the Database Context (DbContext) of the app.

public class CountryContext : DbContext
{
    public CompanyContext(DbContextOptions<CompanyContext> options) : base(options)
    {
    }

    public DbSet<Country> Country { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        //Write Fluent API configurations here
 
        //Entity Configuration
        modelBuilder.Entity<Country>().HasKey(s => s.PId);
 
        //Property Configurations
        modelBuilder.Entity<Country>(entity =>
        {
            entity.Property(e => e.Name)
                  .HasColumnName("CountryName")
                  .HasDefaultValue("USA")
                  .IsRequired();
 
            entity.Property(e => e.AddedOn)
                  .HasColumnType("date")
                  .HasDefaultValueSql("(getdate())");
        });
        modelBuilder.Entity<Country>().Ignore(e => e.population); 
    }
}

In the above code the Country entity is configured in the following manner:

• Line 14 : set it’s PId property as primary key using the HasKey() function.
• Line 19-22 : configured it’s Name property to be set as CountryName on the database table, and it should be a not null column with default value as USA. The IsRequired() method is used to make a column ‘not null’ in the database.
• Line 25, 26 : The AddedOn property is configured to be of date data type with default sql value given by getdate() method.
• Line 28 : The Population will not be mapped to the database table i.e. its column will not be created. The Ignore() method has done this configuration here.

On doing the Entity Framework Core Migrations the Country table will be created on the database which is shown in the below image.

Fluent API Methods

In the below table we have listed down some of the most common methods of Entity Framework Core Fluent API.

“Has/With” Pattern for Configuring Relationships

The Has/With pattern is widely used when configuring relationships with the Fluent API. The Has & With methods must be combined to configure a valid relationship.

There are 2 variants of Has method, these are:

• 1. HasOne
• 2. HasMany

Similarly, there are 2 variants of With method, these are:

• 1. WithOne
• 2. WithMany

The HasOne method along with the WithOne method is used to create Reference Navigation Properties. Similarly, the HasMany method along with the WithMany method is used to create Collection Navigation Properties.

You will learn the usage of these methods in the below 3 tutorials.

• 1. Configure One-to-Many relationship using Fluent API in Entity Framework Core
• 2. Configure One-to-One relationship using Fluent API in Entity Framework Core
• 3. Configure Many-to-Many relationship using Fluent API in Entity Framework Core