c# - 如何像我在 Mysql 查询中执行的那样使用 Linq 执行联合

Question

这就是我如何在两个具有不同列名的不同表之间执行联合， *我只从第二个表中选择日期和金额，并将 null 传递给其余列 *

  string query="select `Date`,`ItemName`,`ReqQty`, `Amount`,`TotalAmount` from ((SELECT s.`Date` ,i.`ItemName`, s.`ReqQty`,s.`Amount`,s.`TotalAmount` FROM `sale` as s join items as i on s.itemid=i.id where s.`partyId`='" + ddllist.SelectedValue.ToString() + "' ) Union all ((select p.date,'','','Recieved', p.`amount` as Totalamount from `OrderPayment` as p where p.`partyId`='" + ddllist.SelectedValue.ToString() + "' ))) tb order by `Date`";

但是在 linq 中我不能创建像 mysql 这样的假列，因为我将 null 传递给我没有的列.. 它给出了错误，这是我的 linq 尝试

       var query1 = (from s in lam.sales where s.PartyId == 1 select new { Date = s.Date, Itemid = s.ItemId, Qty = s.ReqQty, Amount = s.Amount, TotalAmount = s.TotalAmount });

        var query2 = (from q in lam.paydetails where q.partyId == 1 select new { Date =(DateTime?) q.Date, Itemid = 0, Qty = (int?)null, Amount = (int?)null, TotalAmount = q.amount });
        var queryresult = query1.Concat(query2);

销售类

public partial class sale
{
    public int Id { get; set; }
    public int PartyId { get; set; }
    public int ItemId { get; set; }
    public Nullable<int> ReqQty { get; set; }
    public Nullable<int> AvaibleQty { get; set; }
    public string Desc { get; set; }
    public Nullable<int> Amount { get; set; }
    public string Remarks { get; set; }
    public Nullable<System.DateTime> Date { get; set; }
    public int TotalAmount { get; set; }

    public virtual item item { get; set; }
    public virtual partydetail partydetail { get; set; }
}

订单支付类

public partial class orderpayment
{
    public int id { get; set; }
    public Nullable<int> partyId { get; set; }
    public Nullable<decimal> amount { get; set; }
    public Nullable<System.DateTime> Date { get; set; }
    public string Remarks { get; set; }

    public virtual partydetail partydetail { get; set; }
}

ItemClass 引用了 Sales Class 中的 itemId

public partial class item
{
    public item()
    {
        this.sales = new HashSet<sale>();
        this.ordereds = new HashSet<ordered>();
        this.stocks = new HashSet<stock>();
        this.productions = new HashSet<production>();
        this.productions1 = new HashSet<production>();
        this.finishes = new HashSet<finish>();
        this.productions11 = new HashSet<production>();
    }

    public int Id { get; set; }
    public string ItemName { get; set; }
    public string Category { get; set; }
    public string Status { get; set; }
    public Nullable<int> minqty { get; set; }

    public virtual ICollection<sale> sales { get; set; }

}

Answer 1

一些事情要提一下:

(1) SQL联合规则比LINQ宽松。在 LINQ(通常)中，如果所有字段 name 和 type 都匹配，则两个匿名类型被认为是相同的。

(2) SQL to LINQ 联合运算符映射如下:

SQL         LINQ
=========   =======
UNION       Union
UNION ALL   Concat

将它们应用到您的案例中:

var query1 = (from s in lam.sales.AsEnumerable() where s.PartyId == 1
              select new { s.Date, s.item, s.ReqQty, s.Amount, s.TotalAmount });

var query2 = (from q in lam.paydetails where q.partyId == 1
              select new { q.Date, item = "", ReqQty = "", Amount = "", TotalAmount = q.amount });

var queryresult = query1.Concat(query2);

请注意，上面确保字段名称匹配，但您还需要确保类型匹配(因为我没有它们，所以我不能这样做)。例如，如果s.ReqQty 和/或s.Amount 是数字类型，则必须将相应的"" 替换为 null 表示可空类型，0(零)表示不可空类型。

更新:根据您的数据模型类，这里是实际的工作查询:

var query1 = (from s in db.sales where s.PartyId == 1
              select new { s.Date, s.item, s.ReqQty, s.Amount, TotalAmount = (decimal?)s.TotalAmount });

var query2 = (from q in db.paydetails where q.partyId == 1
              select new { q.Date, item = (item)null, ReqQty = (int?)null, Amount = (int?)null, TotalAmount = q.amount });

var queryresult = query1.Concat(query2);