EF核心HasMany vs OwnsMany [英] EF Core HasMany vs OwnsMany

问题描述

对于一对多关系，已有很多和拥有很多有什么区别？我应该何时使用另一个？

For one to many relationship, what's the difference between HasMany and OwnsMany? When should I use one over another?

例如：

public class xxx 
{
    public virtual IReadOnlyCollection<xxxHistoryEntity> Histories => _histories;
    private readonly List<xxxHistoryEntity> _histories = new List<xxxHistoryEntity>();
}

public class xxxHistoryEntity : Entity<string>
{
    public string State { get; set; }
    public string NodeId { get; set; }
    public string Message { get; set; }
}

实体配置：

class xxxConfiguration
    : IEntityTypeConfiguration<xxx>
{
    public void Configure(EntityTypeBuilder<xxx> builder)
    {
        builder.OwnsMany(itm => itm.Histories, collbuilder =>
        {
            collbuilder.HasForeignKey("xxxid");
        });
    }
}

class xxxHistoryConfiguration
    : IEntityTypeConfiguration<xxxHistoryEntity>
{
    public void Configure(EntityTypeBuilder<xxxHistoryEntity> builder)
    {
        builder.ToTable("xxx_histories");
        builder.HasKey(itm => itm.Id);
        builder.Property(itm => itm.Id)
             .ValueGeneratedOnAdd();
    }
}

生成的迁移如下：

        migrationBuilder.CreateTable(
            name: "xxx_histories",
            columns: table => new
            {
                id = table.Column<string>(nullable: false),
                xxxid = table.Column<string>(nullable: false),                    
                state = table.Column<string>(nullable: true),
                nodeid = table.Column<string>(nullable: true),
                message = table.Column<string>(nullable: true),
                xmin = table.Column<uint>(type: "xid", nullable: false)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_xxx_histories", x => new { x.id, x.xxxid });
                table.ForeignKey(
                    name: "fk_xxxhistoryentity_xxx_xxxarid",
                    column: x => x.xxxid,
                    principalTable: "xxx",
                    principalColumn: "id",
                    onDelete: ReferentialAction.Cascade);
            });

如果我通过用HasMany替换OwnsMany来更新 xxxConfiguration ，例如：

if I update the xxxConfiguration by replacing the OwnsMany with HasMany, like:

class xxxConfiguration
    : IEntityTypeConfiguration<xxx>
{
    public void Configure(EntityTypeBuilder<xxx> builder)
    {
        builder.HasMany(itm => itm.Histories)
            .WithOne()
            .HasForeignKey("xxxid");
    }
}

生成的迁移如下：

        migrationBuilder.CreateTable(
            name: "xxx_histories",
            columns: table => new
            {
                id = table.Column<string>(nullable: false),
                xxxid = table.Column<string>(nullable: false),
                state = table.Column<string>(nullable: true),
                nodeid = table.Column<string>(nullable: true),
                message = table.Column<string>(nullable: true),
                xmin = table.Column<uint>(type: "xid", nullable: false)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_xxx_histories", x => new { x.id, x.xxxid });
                table.ForeignKey(
                    name: "fk_xxxhistoryentity_xxx_xxxid",
                    column: x => x.xxxid,
                    principalTable: "xxx",
                    principalColumn: "id",
                    onDelete: ReferentialAction.Cascade);
            });

如您所见，两者生成的迁移是相同的。那么OwnsMany有什么意义呢？

As you can see, the migration generated by both are the same. So what's the point of OwnsMany?

推荐答案

来自文档：

通过

EF Core，您可以对只能出现在其他实体类型的
导航属性中的实体类型进行建模。这些称为拥有的
实体类型。

EF Core allows you to model entity types that can only ever appear on navigation properties of other entity types. These are called owned entity types. The entity containing an owned entity type is its owner.

拥有的实体实质上是所有者的一部分，没有它就不能存在
，它们在概念上类似于

Owned entities are essentially a part of the owner and cannot exist without it, they are conceptually similar to aggregates.

https://docs.microsoft.com/en-us/ef/core/modeling/owned-entities

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