EF Core Indexer properties and Property bag entity types

前言

假設 Entity Class 要提供 Dictionary 的屬性，
可以使用 Indexer Properties，例如，
customer["CustomerType"]。
如果不想在原有的 Table 中新增欄位，
則可以使用 property bag entity types，例如，
customerExt["CustomerType"]
以下我們來看一下做法。

實作

Indexer Properties

customer["CustomerType"]

1.在 Customer Class 中加入 Dictionary

public class Customer
{
    public int Id { get; set; }

    public string FirstName { get;set; }

    public string LastName { get; set; }

    public string FullName => FirstName+ " " + LastName;

    //Indexer Properties
    private readonly Dictionary<string, object> _data = new Dictionary<string, object>();
    public object this[string key]
    {
        get => _data[key];
        set => _data[key]= value;
    }
}

2.在 DbContext 類別中 OnModelCreating Method 設定 IndexerProperty，

public partial class 你的Context: DbContext
{
    // ... other codes ...
    public virtual DbSet<Customer> Customers { get; set; } = null!;

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Customer>(entity =>
        {
            entity.HasKey(e=>e.Id);
            //entity.Property<DateTime>("LastUpdated").HasDefaultValue(new DateTime(2020, 4, 9));
            entity.IndexerProperty<DateTime>("LastUpdated")
                .HasDefaultValue(DateTime.UtcNow);
            entity.IndexerProperty<string>("CustomerType");
        });
    }

}

所以當 update-database 後，Customers 會增加 2 個欄位(LastUpdated 及 CustomerType)

3.存/取值的方式如下，

var _dbContext = new 你的Context();

var customer = _dbContext
    .Customers
    .AsNoTracking()
    .First();

//取值
var customerType = customer["CustomerType"];
var lastUpdated = customer["LastUpdated"];

//要改值
_dbContext.Attach(customer);
customer["CustomerType"] = "VIP";
customer["LastUpdated"] = new DateTime(2020, 4, 9);
//屬性不在會被忽略掉，不會有錯誤
customer["沒欄位"] = "ABC";
_dbContext.SaveChanges();

Property bag entity types

存到另一個　 Class ，例如，
customerExt["CustomerType"]

1.建立 DbSet<Dictionary<string, object>> 及設定 SharedTypeEntity
例如建立 Customers 及 Orders 的擴充 Table(CustomerExts, OrderExts)

public partial class 你的Context: DbContext
{
    // ... other codes ...
    public DbSet<Dictionary<string, object>> CustomerExts => Set<Dictionary<string, object>>("CustomerExts");
    public DbSet<Dictionary<string, object>> OrderExts => Set<Dictionary<string, object>>("OrderExts");

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.SharedTypeEntity<Dictionary<string, object>>(
            "CustomerExts", c =>
            {
                c.Property<int>("Id");
                c.Property<int>("CustomerId");
                c.Property<string>("CustomerType");
                c.Property<DateTime>("LastUpdated");
            });

        modelBuilder.SharedTypeEntity<Dictionary<string, object>>(
            "OrderExts", c =>
            {
                c.Property<int>("Id");
                c.Property<int>("OrderId");
                c.Property<string>("OrderType");
                c.Property<DateTime>("LastUpdated");
            });
        // ... other codes ...
    }

}

2.存取方式如下，

var _dbContext = new 你的Context();
//新增
var newCustomerExt = new Dictionary<string, object>
{
    {"CustomerId", 3 },
    {"CustomerType", "Invalid" },
    {"LastUpdated", new DateTime(2020, 9, 25) }
};
_dbContext.CustomerExts.Add(newCustomerExt);

var newOrderExt = new Dictionary<string, object>
{
    {"OrderId", 1 },
    {"OrderType", "NeedConfirm" },
    {"LastUpdated", new DateTime(2020, 9, 25) }
};
_dbContext.OrderExts.Add(newOrderExt);
_dbContext.SaveChanges();

//更新
var customerExt = _dbContext.CustomerExts.First();
customerExt["CustomerType"] = "VIP";

var orderExt = _dbContext.OrderExts.First();
orderExt["OrderType"] = "Confirmed";

_dbContext.SaveChanges();

DB 就會建立 CustomerExts 及 OrderExts 資料表，

參考資源

陰影和索引子屬性
Indexers