如何在单个事务中持久化具有主细节关系的表

Question

我正在尝试使用Delphi XE3和Zeos 7.0.4在MySQL 5.6中持久化两个具有主-细节关系的表。当我在master上执行ApplyUpdates时，自动递增字段的值保持为0。我需要自动递增值，这样我就可以将详细信息表与来自ApplyUpdates的主表的ID字段链接起来。我使用的ZConnection的AutoCommit=FALSE，TransactionIsolationLevel=tiReadCommitted，ZQuery的CachedUpdates=TRUE。我错过了什么？

ZQPerson.Append;
ZQEmployee.Append;
try
  ZQPersonName.Value := Edit1.Text;
  ZQPerson.ApplyUpdates; //Here I expected to have the auto increment value on the Id field of ZQPerson, but it returns always 0
  ZQEmployeePersonID.Value := ZQPersonId.Value; //Here I'd link Employee to it's Person record
  ZQEmployeeRegNo.Value := StrToInt(Edit2.Text);
  ZQEmployee.ApplyUpdates;
  ZConnection1.Commit; //Here I would persist both tables in a single transaction to avoid master table without details
except
  ZQPerson.CancelUpdates;
  ZQEmployee.CancelUpdates;
  ZConnection1.Rollback; //In case of exceptions rollback everything
  raise;
end;
ZQPerson.CommitUpdates;
ZQEmployee.CommitUpdates;

我的ZSQLMonitor跟踪是这样的：

2013-08-29 00:01:23 cat: Execute, proto: mysql-5, msg: INSERT INTO person (Id, name) VALUES (NULL, 'Edit1') --> This is just after ZQPerson.ApplyUpdates
2013-08-29 00:01:50 cat: Execute, proto: mysql-5, msg: INSERT INTO employee (Id, RegNo, ProductId) VALUES (NULL, 1000, 0), errcode: 1452, error: Cannot add or update a child row: a foreign key constraint fails (`test`.`employee`, CONSTRAINT `FK_A6085E0491BDF8EE` FOREIGN KEY (`PersonId`) REFERENCES `person` (`Id`) --> This is just after ZQEmployee.ApplyUpdates
2013-08-29 00:02:05 cat: Execute, proto: mysql-5, msg: Native Rollback call --> Rollback after Exception on the ZQEmployee.ApplyUpdates

Answer 1

是否使用ZConnection1.StartTransaction启动事务？我也认为你必须在调用ZQuery1.ApplyUpdates后刷新ZQuery1才能获得新的id-

阅读你的评论，你一定是在做一个没有where子句的select*？正确的我可以建议你使用这种方法：

1） 选择并递增当前的自动递增值
2） 从id=[step1 id]//的主表中选择，它当然是空的
3） 使用步骤1中的id添加详细信息
4） 在主数据集中分配id
5） 应用两个更新

Answer 2

我找到的解决方法就是这个。它并没有让我完全满意，因为它没有透明地使用数据库的自动递增功能，让我使用Last_Insert_ID（）函数。我正在与zeos-develpers联系以查看这一点。

function LastInsertID(ATableName: string): Integer;
var DBQuery: TZQuery;
begin
  DBQuery := TZQuery.Create(Self);
  with DBQuery do
  begin
    Connection := ZConnection1;
    SQL.Clear;
    SQL.Add('Select Last_Insert_ID() as Last_Insert_ID from ' + ATableName);
    Open;
    Result := FieldByName('Last_Insert_ID').Value;
    Free;
  end;
end;
procedure Persist;
var LastID: Integer;
begin
  ZQPerson.Append;
  ZQEmployee.Append;
  try
    ZQPersonName.Value := Edit1.Text;
    ZQPerson.ApplyUpdates; // Here I expected to have the auto increment value on the Id field of ZQPerson, but it returns always 0
    LastID := LastInsertID('Person'); //Getting the Last_Insert_ID(), even on the uncommitted transction, works
    ZQEmployeePersonId.Value := LastID; //Link the two tables using the Last_Insert_ID() result
    ZQEmployeeRegNo.Value := StrToInt(Edit2.Text);
    ZQEmployee.ApplyUpdates;
    ZConnection1.Commit; // Here I persist both tables in a single transaction to avoid master table without details
  except
    ZQPerson.CancelUpdates;
    ZQEmployee.CancelUpdates;
    ZConnection1.Rollback; // In case of exceptions rollback everything
    raise;
  end;
  ZQPerson.CommitUpdates;
  ZQEmployee.CommitUpdates;

Answer 3

我在一个简单的数据库中测试了它，该数据库中有两个主表和明细表，它们嵌套在TDataSource中，并通过明细表的where进行关联：

object conMysql: TZConnection
     TransactIsolationLevel = tiReadCommitted
object zqryMaster: TZQuery
     Connection = conMysql
SQL.Strings = (
       'select * from temp.master')
object dsNestedMaster: TDataSource
     DataSet = zqryMaster
object zqryDetail: TZQuery
     Connection = conMysql
     SQL.Strings = (
       'select * from temp.detail'
       'where id_master =: id')

启动事务后，如果出现错误，所有更新都必须等待确认或回滚：

  try
    zqryMaster.Connection.StartTransaction;
    zqryMaster.Edit;
    zqryDetail.Edit;
    zqryMaster.FindField('dt_mov').Value := Now;
    while not zqryDetail.Eof do
    begin
      zqryDetail.Edit;
      zqryDetail.FindField('dt_mov').Value := Now;
      zqryDetail.ApplyUpdates;
      zqryDetail.Next;
      //raise Exception.Create('simple error'); //use for tests, check database after perform
    end;
    zqryMaster.ApplyUpdates;
    zqryMaster.Connection.Commit;
  except
    zqryMaster.Connection.Rollback;
    zqryMaster.CancelUpdates;
    zqryDetail.CancelUpdates;
  end;