问题
I'm playing wit EF Core 2.1 Preview 2.
I have troubles with HasData (Seed) method in OnModelCreating(ModelBuilder modelBuilder)
My model is simple POCO class that has no annotation.
public class Tenant {
public int TenantID {get; set;}
public string Name {get; set;}
}
in my DbContext
inside OnModelCreating
method is DB model defined as
modelBuilder.Entity<Tenant>(e => {
e.HasKey(m => m.TenantID)
.HasName("PK_Tenants");
e.Property(m => m.TenantID)
.UseSqlServerIdentityColumn();
e.Property(m => m.Name)
.IsRequired()
.HasMaxLength(256);
}
and the seed mehod is defined as:
modelBuilder.Entity<Tenant>().HasData(new []{
new Tenant {
TenantID = 0,
Name = "SystemTenant",
}
});
During startap, when ctx.Database.Migrate() is run, I got exception: The seed entity for entity type 'Tenant' cannot be added because there was no value provided for the required property 'TenantID
回答1:
The exception is little bit misleading. There must be some mechanism inside, that tests required properties so they must be different to a default values.
The only change I had to do was specifying TenantID != 0
.
modelBuilder.Entity<Tenant>().HasData(new []{
new Tenant {
TenantID = 1, // Must be != 0
Name = "SystemTenant",
}
});
回答2:
I have created little "hack" to bypass 0 PK value restriction after I reverse engineering the EF Core code and I found this line of code. Related to @Tomino answer. Here is my snipped extension code:
using System;
using System.Linq;
using System.Collections.Generic;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Internal;
using Microsoft.EntityFrameworkCore.Metadata.Internal;
namespace EntityFrameworkCore.CustomMigration
{
public static class CustomModelBuilder
{
public static bool IsSignedInteger(this Type type)
=> type == typeof(int)
|| type == typeof(long)
|| type == typeof(short)
|| type == typeof(sbyte);
public static void Seed<T>(this ModelBuilder modelBuilder, IEnumerable<T> data) where T : class
{
var entnty = modelBuilder.Entity<T>();
var pk = entnty.Metadata
.GetProperties()
.FirstOrDefault(property =>
property.RequiresValueGenerator()
&& property.IsPrimaryKey()
&& property.ClrType.IsSignedInteger()
&& property.ClrType.IsDefaultValue(0)
);
if (pk != null)
{
entnty.Property(pk.Name).ValueGeneratedNever();
entnty.HasData(data);
entnty.Property(pk.Name).UseSqlServerIdentityColumn();
}
else
{
entnty.HasData(data);
}
}
}
}
And you can use it like this in OnModelCreating
method:
protected override void OnModelCreating(ModelBuilder builder)
{
base.OnModelCreating(builder);
builder.Seed(new List<Tenant> {
new Tenant() {TenantID = 0 , Name = string.Empty},
new Tenant() {TenantID = 1 , Name = "test"}
//....
);
//....
}
回答3:
I was using a custom service to pull data to database, I did it like this:
builder.Entity<EntityName>().HasData(someSerive.GetById(id).AsEnumerable());
I got to change it to ToArray()
:
builder.Entity<EntityName>().HasData(someSerive.GetById(id).ToArray());
来源:https://stackoverflow.com/questions/50010613/the-seed-entity-for-entity-type-x-cannot-be-added-because-the-was-no-value-pro