选择带引用的对象时，ServiceStack OrmLite会引发MissingMethodException

Question

我正在尝试跨越两个数据库表的简单选择。我正在从名为PlayerEquipment的关联表中进行选择，如下所示：

 PlayerId | ItemId | Quantity | IsEquipped
----------+--------+----------+------------
 1          1        1          1
 1          3        1          0

这构成了我们系统中玩家的广告资源，映射到Player和Item表格中的特定ID。

关联的PlayerEquipment POCO如下所示：

public class PlayerEquipment
{
    [Ignore]
    public string Id
    {
        get { return PlayerId + "/" + ItemId; }
    }

    public int PlayerId { get; set; }

    [References(typeof(ItemData))]
    public int ItemId { get; set; }

    public int Quantity { get; set; }

    public bool IsEquipped { get; set; }

    [Reference]
    public ItemData ItemData { get; set; }
}

目前，忽略PlayerId与相关Player对象无关的事实（最终会是这样）。

我正在尝试获取一个玩家的设备列表，给出他的ID：

List<PlayerEquipment> equipment = this.Db.LoadSelect<PlayerEquipment>(q => q.PlayerId == playerId);

当我打电话时，我得到了这个例外：

Method not found: 'Boolean ServiceStack.EnumerableExtensions.IsEmpty(System.__Canon[])'.

...使用此堆栈跟踪：

at ServiceStack.OrmLite.OrmLiteReadCommandExtensions.LoadListWithReferences[Into,From](IDbCommand dbCmd, SqlExpression`1 expr, String[] include)
   at ServiceStack.OrmLite.ReadExpressionCommandExtensions.LoadSelect[T](IDbCommand dbCmd, Expression`1 predicate, String[] include)
   at ServiceStack.OrmLite.OrmLiteReadExpressionsApi.<>c__DisplayClass34`1.<LoadSelect>b__33(IDbCommand dbCmd)
   at ServiceStack.OrmLite.OrmLiteExecFilter.Exec[T](IDbConnection dbConn, Func`2 filter)
   at ServiceStack.OrmLite.OrmLiteReadExpressionsApi.Exec[T](IDbConnection dbConn, Func`2 filter)
   at ServiceStack.OrmLite.OrmLiteReadExpressionsApi.LoadSelect[T](IDbConnection dbConn, Expression`1 predicate, String[] include)
   [snip]

在线查看，我没有找到任何有关此异常的帮助，但我无法想象如何让我的查询更简单。我是以错误的方式解决这个问题吗？我应该改为查询引用Player属性的Item或List<PlayerEquipment>对象吗？

Answer 1

我刚刚在所有受支持的数据库中尝试过此示例，并且它按预期工作。唯一的变化是删除主键上不允许的[Ignore]，因为它们需要存在于基础RDBMS表中。

使用的类型

public class PlayerEquipment
{
    public string Id
    {
        get { return PlayerId + "/" + ItemId; }
    }

    public int PlayerId { get; set; }

    [References(typeof(ItemData))]
    public int ItemId { get; set; }

    public int Quantity { get; set; }

    public bool IsEquipped { get; set; }

    [Reference]
    public ItemData ItemData { get; set; }
}

public class ItemData
{
    [AutoIncrement]
    public int Id { get; set; }

    public string Data { get; set; }
}

创建表格，填充数据，选择和转储结果

db.DropTable<PlayerEquipment>();
db.DropTable<ItemData>();

db.CreateTable<ItemData>();
db.CreateTable<PlayerEquipment>();

var item1 = new ItemData { Data = "ITEM1" };
db.Save(item1);

db.Save(new PlayerEquipment
{
    PlayerId = 1,
    ItemId = item1.Id,
    Quantity = 1,
    IsEquipped = true,
});

var item2 = new ItemData { Data = "ITEM2" };
db.Save(item2);

db.Save(new PlayerEquipment
{
    PlayerId = 1,
    ItemId = item2.Id,
    Quantity = 1,
    IsEquipped = false,
});

var playerId = 1;
var results = db.LoadSelect<PlayerEquipment>(q => q.PlayerId == playerId);

results.PrintDump();

控制台输出

[
    {
        Id: 1/1,
        PlayerId: 1,
        ItemId: 1,
        Quantity: 1,
        IsEquipped: True,
        ItemData: 
        {
            Id: 1,
            Data: ITEM1
        }
    },
    {
        Id: 1/2,
        PlayerId: 1,
        ItemId: 2,
        Quantity: 1,
        IsEquipped: False,
        ItemData: 
        {
            Id: 2,
            Data: ITEM2
        }
    }
]