![]() While identity and serial columns set up a sequence for you behind the scenes, sometimes you may want to manage sequence creation yourself. It is not possible to specify sequence options for serial columns, but you can set up a sequence separately and configure the column's default value (see sequence-driven columns). Another strategy is to seed negative values only, allowing your identity column to start at 1. This technique allows to start your identity sequence at a value higher than all seeded data values. Seeded data must explicitly specify all columns - including database-generated ones - but the backing sequence for identity columns isn't aware that the values are in use, and will generate conflicting values. This can be especially useful when seeding data. => modelBuilder.Entity().Property(b => b.Id) For example, the following makes the column values start at 100: protected override void OnModelCreating(ModelBuilder modelBuilder) Identity columns have a standard sequence, managed behind the scenes by PostgreSQL you can customize the sequence options for these. => modelBuilder.Entity().Property(b => b.Id).UseIdentityAlwaysColumn() Regardless of the model default, you can define a value-generation strategy on a property-by-property basis: protected override void OnModelCreating(ModelBuilder modelBuilder) => optionsBuilder.UseNpgsql(".", o => o.SetPostgresVersion(9, 6)) ĭefining the strategy for a single property It is recommended to place the provider in compatibility mode with your specific version - this will also affect the default value generation strategy: protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) Note that if you are using PostgreSQL 9.6 or older, identity columns will not work. For example, to opt out of the change to identity columns, simply place the following in your context's OnModelCreating(): protected override void OnModelCreating(ModelBuilder modelBuilder) You can easily control the value generation strategy for the entire model. Defining the default strategy for the entire model Changing a value generation strategy is a significant change to an existing database. This is a sensitive, one-time migration operation that should be done with care, and carefully tested before deployment to production. Since the default strategy has changed, if you have an existing database with migrations, the the first migration created after upgrading to version 3.0 will alter your tables and convert serial columns to identity ones. a property called Id in your entity) and will implicitly set them to ValueGeneratedOnAdd a standard model with ID columns should automatically get created with the appropriate column type. Note that EF Core will automatically recognize key properties by convention (e.g. In other words, when ValueGeneratedOnAdd is specified on a short, int or long property, the Npgsql provider will automatically map it to a serial or identity column. Prior to version 3.0, the Npgsql provider generates "serial" columns for ID columns starting with version 3.0, it generates "identity by default" instead. Recommended only if you are using an older PostgreSQL version. This will create the column with the serial datatype.
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