EF Core HasMany vs OwnsMany

问题

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

For example:

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; }
}

The Entity Configuration:

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();
    }
}

The generated migration is below:

        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);
            });

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");
    }
}

The generated migration is below:

        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);
            });

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

回答1:

From documentation:

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.

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

来源：https://stackoverflow.com/questions/58516830/ef-core-hasmany-vs-ownsmany

标签

entity-framework

ef-core-2.2