What is the purpose of the ADO.NET _ CommandPtr interface
This article introduces the knowledge of "what is the function of ADO.NET _ CommandPtr interface". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!
The ADO library contains three basic interfaces: the _ ConnectionPtr interface, the _ CommandPtr interface, and the _ RecordsetPtr interface. The ADO.NET _ CommandPtr interface returns a recordset or a null pointer. It is typically used to create a data connection or to execute a SQL statement that returns no results, such as a stored procedure. It is not a good use to return a recordset using the _ ConnectionPtr interface. The operation to return the record is usually implemented with _ RecordserPtr. In order to get the number of records, you have to traverse all records with the _ ConnectionPtr operation, but not with _ RecordserPtr.
The ADO.NET _ CommandPtr interface returns a recordset. It provides a simple way to execute stored procedures and SQL statements that return a recordset. When using the _ CommandPtr interface, you can take advantage of the global _ ConnectionPtr interface, or you can use the connection string directly in the _ CommandPtr interface. If you only perform one or more data access operations, the latter is a better choice. But if you want to access the database frequently and return many recordsets, you should use the global _ ConnectionPtr interface to create a data connection, and then use the _ CommandPtr interface to execute stored procedures and SQL statements.
ADO.NET _ RecordsetPtr is a recordset object. Compared with the above two objects, it provides more control functions to the recordset, such as record locking, cursor control and so on. Like the _ CommandPtr interface, it does not have to use a data connection that has been created. Instead of assigning a connection pointer to the connection member variable of _ RecordsetPtr, you can use a connection string to create its own data connection. If you want to use multiple recordsets, the method is to use the global _ ConnectionPtr interface that has created a data connection like the Command object, and then use _ RecordsetPtr to execute stored procedures and SQL statements.
Using the ADO.NET _ CommandPtr interface, the _ CommandPtr interface returns a Recordset object and provides more recordset control functions. The following code examples the method of using the ADO.NET _ CommandPtr interface:
_ CommandPtr pCommand; _ RecordsetPtr pRs; pCommand.CreateInstance (_ _ uuidof (Command)); pCommand- > ActiveConnection=pConn; pCommand- > CommandText= "select * from student"; pCommand- > CommandType=adCmdText; pCommand- > Parameters- > Refresh (); pRs=pCommand- > Execute (NULL,NULL,adCmdUnknown); _ variant_t varValue = pRs- > GetCollect ("name"); Cstring strValue= (char*) _ bstr_t (varValue)
About data type conversion because the COM object is cross-platform, it uses a general method to deal with various types of data, so the Cstring class and the COM object are not compatible, we need a set of API to convert the COM object and C++ type data. _ vatiant_t and _ bstr_t are two such objects. They provide general methods for converting data of COM objects and C++ types.
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