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This article mainly talks about "what are the ADO classes". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "what are the ADO classes"?

ADO includes six classes: Connection,Command,Recordset,Errors,Parameters,Fields

In 1992, Microsoft, Sybase and Digital jointly established the ODBC standard interface, which uses a single ODBC API to access various databases. Then ODBC gained the support of many database manufacturers and Third-Party and gradually became the standard data access technology.

ODBC is covered by the industry standard specification X/OpenCall-LevelInterface (CLI) and ISO/IEC9075-3Call-LevelInterface (SADO class QL/CLI) at that time, so it supports a wide range of databases. Although ODBC was inefficient and limited in its early versions, it was belittled by people. However, with the continuous improvement of ODBC by Microsoft, the execution efficiency of ODBC is increasing, and the functions of ODBC drivers are becoming more and more complete. Up to now, ODBC is a stable and efficient data access engine.

However, ODBC only supports relational ADO class libraries, as well as traditional database data types, and only provides services in the form of API (API is some C code, is * * layer programs, and some .dll files in windows), so it can not meet the increasingly complex data access applications and can not be used by scripting languages. Therefore, in addition to ODBC, Microsoft also introduces other data access technologies to meet the different needs of programmers. (note: ODBC is a process-oriented language developed by C language, which is not compatible with multiple languages, so it is difficult to develop, and it only supports a limited number of database companies, but not for later EXCEL.)

With the increasing complexity of data sources, today's applications are likely to need to take data from different data sources, process them, and then output the processed data to another data source. The more troublesome thing about the ADO class is that these data sources may not be traditional relational databases, but may be Excel files, electronic signature information on Email,Internet/Intranet. Microsoft to enable applications to access a variety of different numbers in a unified way

According to the source, the UniversalDataAccess (UDA) architecture was proposed in 1997.

UDA takes COM technology as the core to assist program ADO class members to access all kinds of data sources in the enterprise. UDA uses OLE-DB (software that belongs to the operating system level) as the technology skeleton. OLE-DB defines a unified ADO class interface as a standard for accessing all kinds of heterogeneous data sources and encapsulates it in a set of COM objects. With OLE-DB, programmers can access all kinds of data in a consistent way. But OLEDB is still a low-level, low-efficiency.

Although OLE-DB allows programmers to access all kinds of data, it is a very good architecture, but because OLE-DB is too low-level and complex to use, it requires programmers to have great skills, so only a small number of programmers can use OLE-DB. This makes it impossible for OLE-DB to become popular.

In order to solve this problem, and to enable VB and scripting languages to access a variety of data sources through OLE-DB, Microsoft also uses COM technology to encapsulate OLE-DB as ADO objects. (this step is very important, realizing that a variety of programs can adjust each other, and the languages that can be developed are also rich) simplifies the work of programmers' data access. Because ADO successfully encapsulates most of the functions of OLE-DB and greatly simplifies the work of data access, ADO classes are gradually accepted by more and more programmers.

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