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Question

我有多个数据表：我想合并它们（我的 P.K：emp_num ）

var tblEmp_data = new DataTable();//one row
var tblEmp_time = new DataTable();//one row
var tbl_emp_mission = new DataTable();//one row

tblEmp_data = GetEmpInfo(empNum);
tblEmp_time = GetEmpTime(empNum, start_period, end_period);
tbl_emp_mission = GetEmpMission(empNum, start_period, end_period);

tblEmp_data.Merge(tblEmp_time, false, MissingSchemaAction.Add);
tblEmp_data.AcceptChanges();
tblEmp_data.Merge(tbl_emp_mission, false, MissingSchemaAction.Add);
tblEmp_data.AcceptChanges();

现在我获得了多行而不是一行的数据！我希望数据在一行？怎么做？

注意：我希望除主键之外的所有列都允许null，所以我避免了这个异常：

failed to enable constraints. one or more rows contain values violating non-null, unique, or foreign-key constraints

编辑：

导致问题的第三个表：

public static DataTable GetEmpMission(int empNum, DateTime start_period, DateTime end_period)
        {
            using (IfxConnection con = new IfxConnection(ConfigurationManager.ConnectionStrings["tl"].ToString()))
            {
                DataTable dt = new DataTable();
                StringBuilder cmdTxt = new StringBuilder();
                cmdTxt.Append(" SELECT COUNT(emp_num)  ");
                cmdTxt.Append(" FROM hs_mission WHERE emp_num = ? AND from_date BETWEEN ? AND ?  ");

                using (var myIfxCmd = new IfxCommand(cmdTxt.ToString(), con))
                {

                    myIfxCmd.CommandType = CommandType.Text;
                    if (con.State == ConnectionState.Closed)
                    {
                        con.Open();
                    }
                    myIfxCmd.Parameters.Add("emp_num", IfxType.SmallInt);
                    myIfxCmd.Parameters.Add("start_period", IfxType.Date);
                    myIfxCmd.Parameters.Add("end_period", IfxType.Date);

                    myIfxCmd.Parameters[0].Value = ((object)empNum) ?? DBNull.Value;
                    myIfxCmd.Parameters[1].Value = ((object)start_period.Date) ?? DBNull.Value;
                    myIfxCmd.Parameters[2].Value = ((object)end_period.Date) ?? DBNull.Value;

                    using (IfxDataReader dr = myIfxCmd.ExecuteReader())
                    {
                        dt.Load(dr);
                        dt.Columns.Add("emp_num", typeof(Int32));
                        dt.Rows[0]["emp_num"] = empNum;
                        dt.AcceptChanges();
                    }

                }
                con.Close();
                con.Dispose();
                return dt;


            }

        }

返回这样的数据：

column1            emp_num 

 0                   6762

并抛出异常：

failed to enable constraints. one or more rows contain values violating non-null, unique, or foreign-key constraints

Answer 1

所以empNum是所有表共享的关键列？听起来好像可以使用my MergeAll：

public static DataTable MergeAll(this IList<DataTable> tables, String primaryKeyColumn)
{
    if (!tables.Any())
        throw new ArgumentException("Tables must not be empty", "tables");
    if(primaryKeyColumn != null)
        foreach(DataTable t in tables)
            if(!t.Columns.Contains(primaryKeyColumn))
                throw new ArgumentException("All tables must have the specified primarykey column " + primaryKeyColumn, "primaryKeyColumn");

    if(tables.Count == 1)
        return tables[0];

    DataTable table = new DataTable("TblUnion");
    table.BeginLoadData(); // Turns off notifications, index maintenance, and constraints while loading data
    foreach (DataTable t in tables)
    {
        foreach (DataColumn col in t.Columns) 
            col.ReadOnly = false; // this might be required in your case
        table.Merge(t); // same as table.Merge(t, false, MissingSchemaAction.Add);
    }
    table.EndLoadData();

    if (primaryKeyColumn != null)
    {
        // since we might have no real primary keys defined, the rows now might have repeating fields
        // so now we're going to "join" these rows ...
        var pkGroups = table.AsEnumerable()
            .GroupBy(r => r[primaryKeyColumn]);
        var dupGroups = pkGroups.Where(g => g.Count() > 1);
        foreach (var grpDup in dupGroups)
        { 
            // use first row and modify it
            DataRow firstRow = grpDup.First();
            foreach (DataColumn c in table.Columns)
            {
                if (firstRow.IsNull(c))
                {
                    DataRow firstNotNullRow = grpDup.Skip(1).FirstOrDefault(r => !r.IsNull(c));
                    if (firstNotNullRow != null)
                        firstRow[c] = firstNotNullRow[c];
                }
            }
            // remove all but first row
            var rowsToRemove = grpDup.Skip(1);
            foreach(DataRow rowToRemove in rowsToRemove)
                table.Rows.Remove(rowToRemove);
        }
    }

    return table;
}

然后以这种方式使用它：

var tables = new[] { tblEmp_data, tblEmp_time, tbl_emp_mission };
tblEmp_data = tables.MergeAll("empNum");

Answer 2

如果我理解正确，您将拥有三个数据表中的数据，并且每个表都有一个您希望在结果表中具有的列（或多个列）。基本上，每个表都包含一行，并且您希望合并列。

在这种情况下，我只需创建一个新列，然后将值复制到：

void MergeColumns_SO16666297(DataTable destination, DataTable source, IEnumerable<string> columnsToSkip)
{
if(columnsToSkip==null) columnsToSkip= new List<string>();
foreach(var col in source.Columns.OfType<DataColumn>().Where(col=>!columnsToSkip.Contains(col.ColumnName)))
    {
        var newCol = destination.Columns.Add(col.ColumnName, col.DataType);
        newCol.AllowDBNull = true ;
        destination.Rows[0][newCol] = source.Rows[0][col];
    }
}

像这样使用：MergeColumns_SO16666297(tblEmp_data,tblEmp_time,new string[]{"emp_num"});

我的第二个想法是，创建一个TransferObjects类，它包含您需要的所有字段，并从各个表中复制值。

Answer 3

如果您的主键列在所有数据表中具有相同的名称，这应该可以获得一行中的数据

    private DataTable MergeDataTables(List<DataTable> tables)
    {
        //.
        if (null == tables || false == tables.Any())
        {
            return null;
        }

        //.
        DataTable merged = tables.First();

        //.
        for (int i = 1; i < tables.Count; i++)
        {
            var cur = tables[i];

            //.merge columns
            foreach (DataColumn c in cur.Columns)
            {
                if (-1 == merged.Columns.IndexOf(c.ColumnName))
                {
                    merged.Columns.Add(c.ColumnName, c.DataType);
                }
            }

            //.merge rows
            foreach (DataRow r in cur.Rows)
            {
                merged.ImportRow(r);
            }
        }

        //.
        return merged;
    }

如何在一行中合并多个数据表（每个数据表返回一行）

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3 个答案: