播种大量数据（EF Core）

Question

Here is the script which I use manually after the database creating to generate useless data for testing:

DECLARE @index BIGINT

SET @index = 0
SET IDENTITY_INSERT Persons ON

WHILE @index < 50000
BEGIN   
    INSERT INTO Persons
        (Id, [Name], Code)
    VALUES
        (NEWID(), CONCAT('Person', @index), @index)

    SET @index = @index + 1
END

How can I run it using EF core in the moment of the database initialization or somehow using data seeding methods? All the answers around are about small amounts of data, but in my case, I work with ~ 50000 records.

Answer 1

If you are using EF Core 2.1 and higher, then making use of HasData method is an ideal way to add seed data.

We can call it using ModelBuilder object in 'OnModelCreating' method to add the data as part of code first migrations.The data then gets seeded the very first time when a database is scaffold or initialized and migrations are applied.

You can also combine it with Bogus to generate fake data for entities.

Inline is a scenario for creating 50000 objects as stated in question. The program executed successfully without any issues. In fact ef core is intelligent enough to split the data into batch queries of 700-800 objects per batch and push it to database.

Entity:

public class Person
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

    [Required]
    public string FirstName { get; set; }

    public string LastName { get; set; }
}

OnModelCreating

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    int id = 1;
    var fakePersons = new Faker<Person>().StrictMode(true)
        .RuleFor(o => o.Id, f => id++)
        .RuleFor(u => u.FirstName, (f, u) => f.Name.FirstName())
        .RuleFor(u => u.LastName, (f, u) => f.Name.LastName());

    var persons = fakePersons.Generate(50000);

    modelBuilder.Entity<Person>().HasData(persons);
}