Frequently used APIs

Frequently used customizations

Below are some of the frequently used customizations using fluent API

Index

You can specify an index over a column as follows:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>()
        .HasIndex(b => b.Url);
}

Index uniqueness

By default, indexes aren't unique: multiple rows are allowed to have the same value(s) for the index's column set. You can make an index unique as follows:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>()
        .HasIndex(b => b.Url)
        .IsUnique();
}

Attempting to insert more than one entity with the same values for the index's column set will cause an exception to be thrown.

Column names

If you prefer to configure your columns with different names, you can do so as following code snippet:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>()
        .Property(b => b.BlogId)
        .HasColumnName("blog_id");
}

Column data types

You can also configure your columns to specify an exact data type for a column. For example, the following code configures Url as a non-unicode string with maximum length of 200 and Rating as decimal with precision of 5 and scale of 2:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>(
        eb =>
        {
            eb.Property(b => b.Url).HasColumnType("varchar(200)");
            eb.Property(b => b.Rating).HasColumnType("decimal(5, 2)");
        });
}

Precision and Scale

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>()
        .Property(b => b.Score)
        .HasPrecision(14, 2);

    modelBuilder.Entity<Blog>()
        .Property(b => b.LastUpdated)
        .HasPrecision(3);
}

Entity Framework does not do any validation of precision or scale before passing data to the provider. It is up to the provider or data store to validate as appropriate

Keys

You can configure a single property to be the primary key of an entity as follows:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Car>()
        .HasKey(c => c.LicensePlate);
}

Detailed reading

Entity Properties - EF CoreMicrosoftLearn

Keys - EF CoreMicrosoftLearn