Linq的Bug收集

1、Linq的应用过程中，若是一个对DbContext的对象的引用，则会自动产生一个SQL查询，而且此类对象不能和非SQL类型的对象混用，也就是说下列举例不能被正常执行：

DbSet<CouponSupply> couponSupplies = _context.CouponSupplies;
List<SupplyTypeResult> supplyTypes = new List<SupplyTypeResult>();
supplyTypes.Add(new SupplyTypeResult
{
    SupplyTypeId = 2,
    SupplyTypeName = "其他投放方式"
});

IQueryable<CouponSupplyQueryResult> couponSupplyQueryResults = couponSupplies.Join(supplyTypes, p => p.SupplyTypeId, q => q.SupplyTypeId, (p, q) => new CouponSupplyQueryResult
{
    CouponSupplyId = p.CouponSupplyId,
    CouponTypeId = p.CouponTypeId,
    CouponTypeName = q.CouponTypeName,
    CouponFaceValue = p.CouponFaceValue,
    CouponSelfPayMoney = p.CouponSelfPayMoney,
});

上述代码中couponSupplies会产生一个SQL查询，而supplyTypes则是非SQL查询，属于静态值类型数据，两者混用时，会报下列错误：

Unable to create a constatnt value of type "VME.Models.SupplyTypeResult". Only primitive types or enumeration types are supported in this context.

解决该问题可以采用下列方式：

1、先通过couponSupplies.ToList()方法获取List对象，确保需要 Join 的两个对象都是非SQL对象。

2、在通过 Linq 的 Join 方法进行级联获取想要的数据。

具体如下：

DbSet<CouponSupply> couponSupplies = _context.CouponSupplies;
List<SupplyTypeResult> supplyTypes = new List<SupplyTypeResult>();
supplyTypes.Add(new SupplyTypeResult
{
    SupplyTypeId = 2,
    SupplyTypeName = "其他投放方式"
});

List<CouponSupply> couponSupplys = couponSupplies.ToList();
IQueryable<CouponSupplyQueryResult> couponSupplyQueryResults = couponSupplys.Join(supplyTypes, p => p.SupplyTypeId, q => q.SupplyTypeId, (p, q) => new CouponSupplyQueryResult
{
    CouponSupplyId = p.CouponSupplyId,
    CouponTypeId = p.CouponTypeId,
    CouponTypeName = q.CouponTypeName,
    CouponFaceValue = p.CouponFaceValue,
    CouponSelfPayMoney = p.CouponSelfPayMoney,
});

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