MySqlDataReader:DataTable.Fill(reader)抛出ConstraintException

Question

我有两个表orders和orderdetails

表顺序(PK = id,orderno上的UNIQUE索引)

|id|orderno|
| 1|1000   |
| 2|1001   |

table orderdetails(PK = id)

|id|orderid|item|qty|
| 1|      1|ABC |  3|
| 2|      1|XYZ |  4|

现在我想查询数据:

SELECT o.orderno, od.item, od.qty
  FROM orders o

INNER JOIN orderdetails od ON.orderno = od.order

返回:

|orderno|item|qty|
|1000   |ABC |  3|
|1000   |XYZ |  4|

但是,如果我使用以下代码将结果加载到DataTable中,它将失败:

var connectionString = "Server=localhost;Database=orders;Uid=root;";
var commandText = "SELECT o.orderno, od.item, od.qty" + Environment.NewLine +
                  "FROM orders o" + Environment.NewLine +
                  "INNER JOIN orderdetails od ON o.orderno = od.order";

var reader = MySqlHelper.ExecuteReader(connectionString, commandText);
var table = new DataTable("OrdersQuery");
table.Fill(reader); // throws ConstraintException

问题是,那

table.Constraints[0]

是一个UniqueConstraints在orderno列上.可能是因为

reader.GetSchemaTable() 

有一个IsUnique=trueorderno条目(在基表中为true,但对于连接查询不是true).

更糟糕的是,这也无济于事:

table.BeginLoadData(); // msdn docs claim that this should disable constraints
table.Load(reader);
table.EndLoadData();

任何想法如何解决这一问题？

堆栈跟踪:

System.Data.ConstraintException Was Unhandled.
  Message=Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints.
  Source=System.Data
  StackTrace:
       bei System.Data.DataTable.EnableConstraints()
       bei System.Data.DataTable.set_EnforceConstraints(Boolean value)
       bei System.Data.DataTable.EndLoadData()
       bei System.Data.Common.DataAdapter.FillFromReader(DataSet dataset, DataTable datatable, String srcTable, DataReaderContainer dataReader, Int32 startRecord, Int32 maxRecords, DataColumn parentChapterColumn, Object parentChapterValue)
       bei System.Data.Common.DataAdapter.Fill(DataTable[] dataTables, IDataReader dataReader, Int32 startRecord, Int32 maxRecords)
       bei System.Data.Common.LoadAdapter.FillFromReader(DataTable[] dataTables, IDataReader dataReader, Int32 startRecord, Int32 maxRecords)
       bei System.Data.DataTable.Load(IDataReader reader, LoadOption loadOption, FillErrorEventHandler errorHandler)
       bei System.Data.DataTable.Load(IDataReader reader)

Answer 1

我遇到了同样的问题,但是通过使用这篇文章的解决方法解决了这个问题:http://bugs.mysql.com/bug.php？id = 65065(底部):

cmd.CommandText = "SELECT cam.no_serie, t.mnt FROM trx t LEFT JOIN camn cam USING(id_camn) ";
    MySqlDataReader dr = cmd.ExecuteReader();
    DataSet ds = new DataSet();
    DataTable dataTable = new DataTable();
    ds.Tables.Add(dataTable);
    ds.EnforceConstraints = false;
    dataTable.Load(dr);
    dr.Close();

Answer 2

我只想通了

table.Fill(reader)

如果我已经添加了列,则不会创建约束.

所以我通过一个很好的小扩展方法修复了这个问题:

    public static void Load(this DataTable table, IDataReader reader, bool createColumns)
    {

        if (createColumns)
        {
            table.Columns.Clear();
            var schemaTable = reader.GetSchemaTable();
            foreach (DataRowView row in schemaTable.DefaultView)
            {
                var columnName = (string)row["ColumnName"];
                var type = (Type)row["DataType"];
                table.Columns.Add(columnName, type);
            }
        }

        table.Load(reader);
    }

用法:

table.Fill(reader, true);