c# - 如何使用从表中选择的字符串？

Question

如何使用从表中选择的字符串？例子：

转换此查询：

 DBEntities MyDB = new DBEntities();
        var Query1 = from P in MyDB.Per
        where P.IDRANK == 2
        select P;
to:


 string strquery = "where P.IDRANK == 2";
    DBEntities MyDB = new DBEntities();
    var Query1 = from P in MyDB.Per
         strquery 
    select P;

Answer 1

如果您可以获得 DataTable，请执行以下操作：

// Build a data table and add columns
DataTable dt = new DataTable();
dt.Columns.Add("IDRank");
dt.Columns.Add("Blah");

// Add rows to the table
for (int i = 1; i < 5; i++) {
    DataRow dr = dt.NewRow();
    dr["IDRank"] = i;
    dr["Blah"] = "Blah" + i.ToString();
    dt.Rows.Add(dr);
}           

// Get a DataView to table
DataView dv = dt.AsDataView();

// Define the filter
string filter = "IDRank = 2";

// Apply the filter
dv.RowFilter = filter;

// Run the query
var Query1 = from P in dv.ToTable().AsEnumerable() select P;

Answer 2

每个表，我都在写很多函数。我需要将这些转换为一个函数。
例如：我有两个 Table Per 功能

private void SelectByRank(int Rank)
        {
            DBEntities MyDB = new DBEntities();
            var Query1 = from P in MyDB.Per
                         where P.IDRANK == Rank
                         select P;
        }
        private void SelectByRankANDBlah(int Rank, string Blah)
        {
            DBEntities MyDB = new DBEntities();
            var Query1 = from P in MyDB.Per
                         where P.IDRANK == Rank && P.BLAH == Blah
                         select P;
        }     

现在，我将转换为一个函数。例如

private void Select(string strKind,int Rank, string Blah)
        {
            var strWhere ="";
            if(strKind == "RANK")
            {
                strWhere  = "where P.IDRANK ==" + Rank;
            }
            else 
            {
                strWhere  = "where P.IDRANK == " + Rank + " && P.BLAH == " + Blah;
            }

            DBEntities MyDB = new DBEntities();
            var Query1 = from P in MyDB.Per
                            strWhere 
                         select P;
        }

好的？

Answer 3

我使用此代码

using (var context = new DBEntities())
            {
                System.Data.Objects.ObjectQuery<User> contacts = context.Users.Where("it.FirstName = @fname", new System.Data.Objects.ObjectParameter("fname", "Arash"));
                List<User> items = contacts.ToList();
            }