合并数据表时的，报错提示问题；

Question

这段代码，是将第一个数据表的“产品名称、规格和目标值”，与第二个数据表的，各产品的出入库数量，合并起来，但在实际执行过程中，使用该方法时，报错提示无效的转换，请问是什么原因呢，在实际查询中，会有在第一个数据表内，有的产品名称、规格和目标值等信息，但在第二出入库的数据表内，因出入库数量是零，所以查询不显示的情况，请问是否与此有关呢，怎么解决这个无效转换的报错问题呢；

```c#
  private DataTable MergeTable(DataTable dt1, DataTable dt2)
  {
      DataTable mergedTable = new DataTable();
      mergedTable.Columns.Add("proName", typeof(string));
      mergedTable.Columns.Add("spec", typeof(string));
      mergedTable.Columns.Add("target", typeof(float));
      mergedTable.Columns.Add("DayInAmount", typeof(decimal));
      mergedTable.Columns.Add("MonthInAmount", typeof(decimal));
      mergedTable.Columns.Add("YearInAmount", typeof(decimal));
      mergedTable.Columns.Add("DayOutAmount", typeof(decimal));
      mergedTable.Columns.Add("MonthOutAmount", typeof(decimal));
      mergedTable.Columns.Add("YearOutAmount", typeof(decimal));

      var mergedRows = from row1 in dt1.AsEnumerable()
                       join row2 in dt2.AsEnumerable()
                       on new { proName = row1.Field<string>("proName").Trim(), spec = row1.Field<string>("spec").Trim() }
                       equals new { proName = row2.Field<string>("proName").Trim(), spec = row2.Field<string>("Fmodel").Trim() }
                       into gj
                       from subRow2 in gj.DefaultIfEmpty()
                       select new
                       {
                           proName = row1.Field<string>("proName").Trim(),
                           spec = row1.Field<string>("spec").Trim(),
                           target = row1.IsNull("target") ? 0f : row1.Field<float>("target"),
                           DayInAmount = subRow2 == null || subRow2.IsNull("DayInAmount") ? 0m : subRow2.Field<decimal>("DayInAmount"),
                           MonthInAmount = subRow2 == null || subRow2.IsNull("MonthInAmount") ? 0m : subRow2.Field<decimal>("MonthInAmount"),
                           YearInAmount = subRow2 == null || subRow2.IsNull("YearInAmount") ? 0m : subRow2.Field<decimal>("YearInAmount"),
                           DayOutAmount = subRow2 == null || subRow2.IsNull("DayOutAmount") ? 0m : subRow2.Field<decimal>("DayOutAmount"),
                           MonthOutAmount = subRow2 == null || subRow2.IsNull("MonthOutAmount") ? 0m : subRow2.Field<decimal>("MonthOutAmount"),
                           YearOutAmount = subRow2 == null || subRow2.IsNull("YearOutAmount") ? 0m : subRow2.Field<decimal>("YearOutAmount")
                       };


      // Add the merged rows to the new DataTable
      foreach (var row in mergedRows)
      {
          mergedTable.Rows.Add(row.proName, row.spec, row.target, row.DayInAmount, row.MonthInAmount, row.YearInAmount, row.DayOutAmount,
                               row.MonthOutAmount, row.YearOutAmount);
      }

      return mergedTable;
  }

```

Answer 1

找到原因了，将数据库对应的字段类型，由float改为real，就可以正常转换了；