如何向由 IDataReader 填充的表添加新行？
在使用 IDataReader 对象（具体来说是 DbDataReader）中包含的信息加载它之后，我试图向 DataTable 添加一个新条目。我认为加载顺利并且对数据库的查询是正确的。
当尝试添加新行时，我收到一个 ArgumentException ，其中包含以下信息：
Cannot set column 'ID'. The value violates the MaxLength limit of this column.
这是我现在拥有的代码：
// Build the query:
DbCommand cmd = dbCon.CreateCommand();
cmd.CommandText = "SELECT ID, Name || ' ' || SurName AS FullName FROM Clients ORDER BY FullName;";
// Execute it:
DbDataReader reader = cmd.ExecuteReader();
// Construct the table out of the query result:
DataTable table = new DataTable();
table .Load(reader);
table.Rows.Add(0, "None");
在数据库（SQLite）中 ID 的类型为 < code>INTEGER 且 Name 和 SurName 都是 VARCHAR。我做错了什么吗？ 0 怎么可能违反 MaxLength 限制？
I'm trying to add a new entry to a DataTable after I load it with the info contained in an IDataReader object, a DbDataReader concretely. The loading goes fine and the query to the database is correct I think.
When trying to add a new row I get an ArgumentException with the following info:
Cannot set column 'ID'. The value violates the MaxLength limit of this column.
This is the code I have right now:
// Build the query:
DbCommand cmd = dbCon.CreateCommand();
cmd.CommandText = "SELECT ID, Name || ' ' || SurName AS FullName FROM Clients ORDER BY FullName;";
// Execute it:
DbDataReader reader = cmd.ExecuteReader();
// Construct the table out of the query result:
DataTable table = new DataTable();
table .Load(reader);
table.Rows.Add(0, "None");
In the database (SQLite) ID is of type INTEGER and both Name and SurName are VARCHARs. Am I doing something wrong? How could 0 violate the MaxLength limit?
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最后，您通过使用我最喜欢的调试器“技巧”之一来消除奇怪的
DataTable异常，解决了该问题。来自评论：由于我正在使用
DbDataAdapter.Fill(DataTable)< /a> 在几乎所有情况下，我都忘记了DataTable.Load(IDataReader)根据导入的IDataReader的结果集推断架构。当然，它至少需要一个DataRow才能做到这一点。这就是为什么它在DataTable不为空时起作用的原因。Finally you've solved the issue by using one of my favourite debugger "tricks" to un-mistify strange
DataTableexceptions. From comments:Since i'm using
DbDataAdapter.Fill(DataTable)in almost all cases, i've forgotten thatDataTable.Load(IDataReader)infers the schema based on the result set from the importedIDataReader. But of course it needs at least oneDataRowto do so. That was the reason why it works when theDataTablewasn't empty.检查数据表中 ID 列的 MaxLength 属性
http://forums.asp.net/t/ 306971.aspx
Check the MaxLength property on your ID column in your datatable
http://forums.asp.net/t/306971.aspx