Linq to Entity 查询需要很长时间才能执行

Question

我是 linq 查询新手，下面显示的 linq 查询需要很长时间才能执行，

List<InventoyModel> vehic = new List<InventoyModel>();

vehic = Winv.Select(x => new InventoyModel
{
    InvID = x.Id,
    WeaponBrand = WH.LKP_WeaponBrand.Where(b => b.BrandID == x.WeaponBrand).Select(b => b.BrandName).FirstOrDefault(),
    LKP_WeaponBrand = x.WeaponBrand,
    weaponModel = WH.LKP_WeaponModel.Where(m => m.ModelID == x.weaponModel).Select(b => b.ModelName).FirstOrDefault(),
    LKP_WeaponModel = x.weaponModel,
    WeaponType = WH.LKP_WeaponType.Where(b => b.TypeID == x.WeaponType).Select(b => b.WeaponName).FirstOrDefault(),
    EntityCategoryID = x.EntityCategoryID,
    // LKP_WeaponType=x.WeaponType,
    SerialNo = x.Serial,
    //LKP_WeaponSerial=x.Serial,
    MadeOf = WH.LKP_BrandOrigin.Where(b => b.ID == x.MadeOf).Select(b => b.CountryName).FirstOrDefault(),
    // LKP_BrandOrigin=Convert.ToInt32(x.MadeOf),
    BulletCount = x.BuletCount,
    AssignerCategoryID = x.AssignerCategoryID,
    WeaponNote = x.Note,
    EntityType = x.EntityType,
    AssignedBy = x.AssignedBy,
    EntityStatusName = WH.LKP_EntityStatus.Where(l => l.StatusID == x.EntityStatus).Select(l => l.Status).FirstOrDefault(),
    IsFile = x.IsFile,
    MarkazName = x.MarkazName,
    MahafzaName = x.MahafzaName,
    NID = x.EmpId.ToString().Trim(),
    Datetime = x.Date,
    UpdateDate = x.ModifyDate,
    ModifierName = x.ModifyBy,
    EntityQty = x.WeaponQty,
    SCEntityQty = 0
}).ToList();

我知道实际上我在查询中使用了许多查询来获取产生问题的值，但我不知道如何解决它。

希望您的建议 谢谢

Answer 1

您的原始查询产生 5 个 OUTER APPLY 查询，这是无效的。因为它看起来像是在主键上连接，所以我们可以用 LEFT JOIN 替换它们。

var query = 
    from x in Winv
    from wb in WH.LKP_WeaponBrand.Where(wb => wb.BrandID == x.WeaponBrand).DefaultIfEmpty()
    from wm in WH.LKP_WeaponModel.Where(wm => wm.ModelID == x.weaponModel).DefaultIfEmpty()
    from wt in WH.LKP_WeaponType.Where(wt => wt.TypeID == x.WeaponType).DefaultIfEmpty()
    from bo in WH.LKP_BrandOrigin.Where(bo => bo.ID == x.MadeOf).DefaultIfEmpty()
    from es in WH.LKP_EntityStatus.Where(es => es.StatusID == x.EntityStatus).DefaultIfEmpty()
    select new InventoyModel
    {
        InvID = x.Id,
        WeaponBrand = wb.BrandName,
        LKP_WeaponBrand = x.WeaponBrand,
        weaponModel = wm.ModelName,
        LKP_WeaponModel = x.weaponModel,
        WeaponType = wt.WeaponName,
        EntityCategoryID = x.EntityCategoryID,
        // LKP_WeaponType=x.WeaponType,
        SerialNo = x.Serial,
        //LKP_WeaponSerial=x.Serial,
        MadeOf = bo.CountryName,
        // LKP_BrandOrigin=Convert.ToInt32(x.MadeOf),
        BulletCount = x.BuletCount,
        AssignerCategoryID = x.AssignerCategoryID,
        WeaponNote = x.Note,
        EntityType = x.EntityType,
        AssignedBy = x.AssignedBy,
        EntityStatusName = es.Status,
        IsFile = x.IsFile,
        MarkazName = x.MarkazName,
        MahafzaName = x.MahafzaName,
        NID = x.EmpId.ToString().Trim(),
        Datetime = x.Date,
        UpdateDate = x.ModifyDate,
        ModifierName = x.ModifyBy,
        EntityQty = x.WeaponQty,
        SCEntityQty = 0
    };

var vehic = query.ToList();

考虑在模型类中引入导航属性。这将简化查询并消除连接的需要。通过适当的导航属性，可以简化您的查询：

var query = Winv
    .Select(x => new InventoyModel
    {
        InvID = x.Id,
        WeaponBrand = x.Brand.BrandName,
        LKP_WeaponBrand = x.WeaponBrand,
        weaponModel = x.Model.ModelName,
        LKP_WeaponModel = x.weaponModel,
        WeaponType = x.Weapon.WeaponName,
        EntityCategoryID = x.EntityCategoryID,
        // LKP_WeaponType=x.WeaponType,
        SerialNo = x.Serial,
        //LKP_WeaponSerial=x.Serial,
        MadeOf = x.MadeOfOrigin.CountryName,
        // LKP_BrandOrigin=Convert.ToInt32(x.MadeOf),
        BulletCount = x.BuletCount,
        AssignerCategoryID = x.AssignerCategoryID,
        WeaponNote = x.Note,
        EntityType = x.EntityType,
        AssignedBy = x.AssignedBy,
        EntityStatusName = x.EntityStatus.Status,
        IsFile = x.IsFile,
        MarkazName = x.MarkazName,
        MahafzaName = x.MahafzaName,
        NID = x.EmpId.ToString().Trim(),
        Datetime = x.Date,
        UpdateDate = x.ModifyDate,
        ModifierName = x.ModifyBy,
        EntityQty = x.WeaponQty,
        SCEntityQty = 0
    });

var vehic = query.ToList();