Entity Framework Core: Fluent API

Here are notes explaining Entity Framework Core (EF Core) Fluent API based on the provided code:

EF Core Fluent API Notes

Overview

• Fluent API provides a way to configure domain classes for the database schema and relationships.

• It offers more control and flexibility than Data Annotations.

• Fluent API configurations are usually done by implementing IEntityTypeConfiguration for each entity.

Entity Configuration Example

• For each entity, create a configuration class implementing IEntityTypeConfiguration.

• Implement the Configure method where you configure properties, keys, relationships, and other aspects.

Key Configuration Topics

1. Property Configuration

• Use Property() to configure entity properties.

• Example configurations:

  • HasMaxLength(50) limits string length to 50 characters.

  • IsRequired() enforces non-nullability.

  • HasColumnName("ColumnName") customizes column names.

  • Ignore() excludes a property from mapping.

Example:

modelBuilder.Property(u => u.FirstName).HasMaxLength(50);
modelBuilder.Property(u => u.FirstName).IsRequired();
modelBuilder.Ignore(u => u.FullName);

2. Primary Key Configuration

• Use HasKey() to specify primary key(s).

• Composite keys are created by passing multiple key properties as anonymous type.

Example:

modelBuilder.HasKey(u => u.Author_Id);
modelBuilder.HasKey(u => new { u.Author_Id, u.Book_Id }); // Composite key

3. Table Name Customization

• Use ToTable("TableName") to map an entity to a different table name.

Example:

modelBuilder.ToTable("Fluent_BookDetails");

4. Relationships Configuration

• One-to-Many: Use HasOne().WithMany().HasForeignKey() to configure one-to-many relationships.

Example:

modelBuilder.HasOne(u => u.Publisher).WithMany(u => u.Books)
    .HasForeignKey(u => u.Publisher_Id);

• Many-to-Many with join entity: Use composite key on join entity and configure two one-to-many relationships.

Example:

modelBuilder.HasKey(u => new { u.Author_Id, u.Book_Id });
modelBuilder.HasOne(u => u.Book).WithMany(u => u.BookAuthorMap)
    .HasForeignKey(u => u.Book_Id);
modelBuilder.HasOne(u => u.Author).WithMany(u => u.BookAuthorMap)
    .HasForeignKey(u => u.Author_Id);

• One-to-One: Use HasOne().WithOne().HasForeignKey() for one-to-one relationships.

Example:

modelBuilder.HasOne(b => b.Book).WithOne(b => b.BookDetail)
    .HasForeignKey(u => u.Book_Id);

Summary of Configurations for Each Entity

How to Apply Configurations

In your DbContext's OnModelCreating method, apply configurations like this:

modelBuilder.ApplyConfiguration(new FluentAuthorConfig());
modelBuilder.ApplyConfiguration(new FluentBookAuthorMapConfig());
modelBuilder.ApplyConfiguration(new FluentBookConfig());
modelBuilder.ApplyConfiguration(new FluentBookDetailConfig());
modelBuilder.ApplyConfiguration(new FluentPublisherConfig());

Additional Notes

• Properties decorated with [NotMapped] are ignored in Fluent configuration with Ignore().

• Composite keys require explicitly declaring all key properties with HasKey().

• Fluent API allows configuring foreign key names and navigation properties explicitly.

• Custom table and column names improve control over the database schema.

These notes summarize the core concepts demonstrated in your EF Core Fluent API configuration code. They provide a good foundation for understanding how to map your domain models to the database schema effectively.