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Data Access Object in VB 6.0 PDF: How to Create and Manipulate Data with DAO


Data Access Object in VB 6.0 PDF: A Comprehensive Guide




If you are a Visual Basic developer who works with databases, you might have heard of Data Access Object (DAO) as a way to access and manipulate data. But what exactly is DAO and how can you use it in your VB 6.0 projects? And more importantly, how can you generate PDF reports with DAO in VB 6.0?




Data Access Object In Vb 6.0 Pdf



In this article, we will answer these questions and more. We will explain what DAO is, what VB 6.0 is, and why you should use DAO in VB 6.0. We will also show you how to install and configure DAO in VB 6.0, how to use DAO to perform various database operations, and how to generate PDF reports with DAO in VB 6.0.


By the end of this article, you will have a clear understanding of DAO in VB 6.0 and how to use it effectively in your projects.


What is Data Access Object (DAO)?




Data Access Object (DAO) is a programming interface that allows you to access and manipulate data stored in various types of databases, such as Microsoft Access, SQL Server, Oracle, MySQL, etc.


DAO provides a set of objects, methods, properties, and events that enable you to perform common database tasks, such as creating, opening, closing, querying, updating, deleting, and reporting data.


DAO is one of the data access technologies that Microsoft provides for Visual Basic developers. Other data access technologies include ActiveX Data Objects (ADO), Remote Data Objects (RDO), OLE DB, and ODBC.


What is Visual Basic 6.0 (VB 6.0)?




Visual Basic 6.0 (VB 6.0) is a programming language and integrated development environment (IDE) that was released by Microsoft in 1998. It is the sixth and final version of the classic Visual Basic language before it was replaced by Visual Basic .NET in 2002.


VB 6.0 is a popular language for developing Windows-based applications that have graphical user interfaces (GUIs), such as forms, menus, toolbars, buttons, etc.


VB 6.0 also supports object-oriented programming (OOP), which allows you to create reusable components called classes that have properties, methods, and events.


VB 6.0 also supports various features that make it easy to work with databases, such as data-bound controls, data-aware controls, data environments, data reports, etc.


Why use DAO in VB 6.0?




There are several reasons why you might want to use DAO in your VB 6.0 projects:


  • DAO is simple and easy to use. You don't need to write complex code or deal with low-level details of database connectivity and communication. You can use DAO objects and methods to perform database tasks with a few lines of code.



  • DAO is fast and efficient. DAO uses direct access to the database engine, which means it bypasses the intermediate layers of ODBC or OLE DB. This results in faster performance and lower overhead.



  • DAO is compatible and flexible. DAO supports a wide range of database types and formats, such as Microsoft Access, SQL Server, Oracle, MySQL, etc. You can also use DAO to access data stored in non-database sources, such as text files, Excel files, etc.



  • DAO is powerful and versatile. DAO allows you to use SQL queries to manipulate data, which gives you more control and flexibility over the data operations. You can also use DAO to create and modify database structures, such as tables, fields, indexes, etc.



  • DAO is integrated and convenient. DAO is built into VB 6.0, which means you don't need to install any additional components or libraries to use it. You can also use DAO with other VB 6.0 features, such as data-bound controls, data-aware controls, data environments, data reports, etc.



How to Install and Configure DAO in VB 6.0




Before you can use DAO in your VB 6.0 projects, you need to install and configure it properly. Here are the steps you need to follow:


Download and Install DAO




The latest version of DAO is 3.6, which was released in 2000. You can download it from the Microsoft website: https://www.microsoft.com/en-us/download/details.aspx?id=5793


After downloading the file (dao360.exe), run it and follow the instructions to install DAO on your computer.


Add DAO Reference to VB Project




After installing DAO, you need to add a reference to it in your VB project. This will enable you to use the DAO objects and methods in your code.


To add a DAO reference, open your VB project and go to Project > References. In the References dialog box, scroll down and check the box next to "Microsoft DAO 3.6 Object Library". Click OK to close the dialog box.


Set DAO Properties and Options




After adding a DAO reference, you need to set some properties and options for DAO in your VB project. This will ensure that DAO works correctly and efficiently in your project.


To set DAO properties and options, go to Tools > Options. In the Options dialog box, click on the Advanced tab. Under Data Access Options, make sure that the following settings are selected:


  • Use Jet for Access databases



  • Use ODBC Cursor Library



  • Use Rowset Objects for Database Objects



  • Use Transactional Processing



Click OK to close the dialog box.


How to Use DAO in VB 6.0




Now that you have installed and configured DAO in your VB project, you are ready to use it to access and manipulate data in your databases. Here are some of the common tasks that you can perform with DAO:


Create a Database Object




The first step to use DAO is to create a Database object. A Database object represents a connection to a specific database file or source.


To create a Database object, you need to use the OpenDatabase method of the DBEngine object. The DBEngine object is a global object that provides access to the database engine and its features.


The OpenDatabase method takes two parameters: the name of the database file or source, and an optional boolean value that indicates whether the database is opened exclusively or not.


For example, the following code creates a Database object that connects to an Access database file named "MyDB.mdb" in the same folder as the VB project:



Dim db As Database Set db = DBEngine.OpenDatabase("MyDB.mdb")


Open and Close a Database Connection




After creating a Database object, you need to open and close the database connection properly.


To open a database connection, you simply need to create a Database object as shown above. The OpenDatabase method automatically opens the connection for you.


To close a database connection, you need to use the Close method of the Database object. The Close method terminates the connection and releases any resources associated with it.


Dim db As Database Set db = DBEngine.OpenDatabase("MyDB.mdb") db.Close


It is a good practice to close the database connection as soon as you are done with it. This will prevent any potential errors or conflicts with other users or applications that might access the same database.


Perform CRUD Operations on Database Tables




One of the main tasks that you can perform with DAO is to perform CRUD operations on database tables. CRUD stands for Create, Read, Update, and Delete, which are the basic operations that you can perform on any data.


To perform CRUD operations on database tables, you need to use the Recordset object. A Recordset object represents a set of records that are retrieved from a database table or query.


To create a Recordset object, you need to use the OpenRecordset method of the Database object. The OpenRecordset method takes two parameters: the name of the table or query that you want to access, and an optional constant that indicates the type of recordset that you want to create.


There are three types of recordsets that you can create with DAO:


  • Table-type recordsets: These are recordsets that directly access a table in the database. They allow you to add, edit, and delete records in the table. They also support indexes and bookmarks for faster navigation and sorting.



  • Dynaset-type recordsets: These are recordsets that are based on a query that can include multiple tables and joins. They allow you to view and edit records that match the query criteria. They also reflect any changes made to the underlying data by other users or applications.



  • Snapshot-type recordsets: These are recordsets that are based on a query that can include multiple tables and joins. They allow you to view records that match the query criteria. However, they do not allow you to edit or delete records, and they do not reflect any changes made to the underlying data by other users or applications.



For example, the following code creates a table-type recordset that accesses a table named "Customers" in the database:



Dim rs As Recordset Set rs = db.OpenRecordset("Customers", dbOpenTable)


The following code creates a dynaset-type recordset that accesses a query named "OrdersByDate" in the database:



Dim rs As Recordset Set rs = db.OpenRecordset("OrdersByDate", dbOpenDynaset)


The following code creates a snapshot-type recordset that accesses a query named "ProductsByCategory" in the database:



Dim rs As Recordset Set rs = db.OpenRecordset("ProductsByCategory", dbOpenSnapshot)


After creating a Recordset object, you can use various methods and properties to perform CRUD operations on the records. Here are some of the common methods and properties that you can use:



  • MoveFirst, MoveLast, MoveNext, MovePrevious: These methods allow you to move to the first, last, next, or previous record in the recordset.



  • EOF, BOF: These properties indicate whether you have reached the end or beginning of the recordset.



  • AddNew: This method allows you to add a new record to the recordset.



  • Edit: This method allows you to edit an existing record in the recordset.



  • Delete: This method allows you to delete an existing record from the recordset.



  • Update: This method allows you to save any changes made to a record in the recordset.



  • CancelUpdate: This method allows you to cancel any changes made to a record in the recordset.



  • Fields: This property returns a collection of Field objects that represent the fields in the recordset. You can use the Fields property to access or modify the values of each field in a record.



  • FindFirst, FindLast, FindNext, FindPrevious: These methods allow you to search for a record that matches a specified criteria in the recordset.



  • Sort: This property allows you to sort the records in the recordset by one or more fields.



  • Filter: This property allows you to filter the records in the recordset by one or more criteria.



For example, the following code loops through the records in the "Customers" table and displays their names and phone numbers:



rs.MoveFirst Do While Not rs.EOF MsgBox "Name: " & rs.Fields("Name") & " Phone: " & rs.Fields("Phone") rs.MoveNext Loop


The following code adds a new record to the "Customers" table with some sample data:



rs.AddNew rs.Fields("Name") = "John Smith" rs.Fields("Phone") = "123-456-7890" rs.Fields("Address") = "123 Main Street" rs.Fields("City") = "New York" rs.Fields("State") = "NY" rs.Fields("Zip") = "10001" rs.Update


The following code edits the phone number of the first record in the "Customers" table:



rs.MoveFirst rs.Edit rs.Fields("Phone") = "987-654-3210" rs.Update


The following code deletes the last record in the "Customers" table:



rs.MoveLast rs.Delete


The following code finds the record in the "Customers" table that has the name "Mary Jones":



rs.FindFirst "Name = 'Mary Jones'" If Not rs.NoMatch Then MsgBox "Record found." Else MsgBox "Record not found." End If


The following code sorts the records in the "Customers" table by name in ascending order:



rs.Sort = "Name"


The following code filters the records in the "Customers" table by state and zip code:



rs.Filter = "State = 'NY' And Zip = '10001'"


Use SQL Queries with DAO




Another task that you can perform with DAO is to use SQL queries to access and manipulate data in your databases. SQL stands for Structured Query Language, which is a standard language for interacting with relational databases.


SQL queries allow you to specify what data you want to retrieve, insert, update, or delete from your databases. You can also use SQL queries to create, modify, or drop database structures, such as tables, fields, indexes, etc.


To use SQL queries with DAO, you need to use the Execute method of the Database object. The Execute method takes two parameters: the SQL statement that you want to execute, and an optional constant that indicates how the statement should be executed.


There are two types of SQL statements that you can execute with DAO:


  • Data Definition Language (DDL) statements: These are statements that create, modify, or drop database structures, such as tables, fields, indexes, etc.



  • Data Manipulation Language (DML) statements: These are statements that retrieve, insert, update, or delete data from database tables or queries.



For example, the following code executes a DDL statement that creates a new table named "Products" in the database:



db.Execute "CREATE TABLE Products (ID Integer Primary Key, Name Text(50), Price Currency)"


The following code executes a DML statement that inserts a new record into the "Products" table with some sample data:



db.Execute "INSERT INTO Products (ID, Name, Price) VALUES (1, 'Laptop', 999.99)"


The following code executes a DML statement that updates the price of the product with ID 1 in the "Products" table:



db.Execute "UPDATE Products SET Price = 899.99 WHERE ID = 1"


The following code executes a DML statement that deletes the product with ID 1 from the "Products" table:



db.Execute "DELETE FROM Products WHERE ID = 1"


The following code executes a DML statement that retrieves all records from the "Products" table and displays their names and prices:



Dim rs As Recordset Set rs = db.Execute("SELECT Name, Price FROM Products") Do While Not rs.EOF MsgBox "Name: " & rs.Fields("Name") & " Price: $" & rs.Fields("Price") rs.MoveNext Loop


Handle Errors and Exceptions with DAO




DAO in your VB 6.0 projects. Errors and exceptions are unexpected or undesirable situations that might arise during the execution of your code, such as invalid input, missing files, network failures, database corruption, etc.


When an error or exception occurs, DAO will raise an error object that contains information about the error, such as the error number, the error description, the source of the error, and the help context for the error.


To handle errors and exceptions with DAO, you need to use the On Error statement and the Err object in your VB code. The On Error statement allows you to specify what action to take when an error occurs. The Err object allows you to access the properties and methods of the error object that DAO raises.


There are three types of actions that you can specify with the On Error statement:


  • On Error GoTo label: This action allows you to transfer the control to a specific line of code that is labeled with a name. This line of code usually contains an error handler that performs some tasks to deal with the error, such as displaying a message, logging the error, or terminating the program.



  • On Error Resume Next: This action allows you to ignore the error and continue with the next line of code. This action is useful when you want to skip over minor errors that do not affect the overall functionality of your program.



  • On Error GoTo 0: This action allows you to reset the error handler and restore the default behavior of VB. This action is useful when you want to end an error handler and resume normal execution.



For example, the following code uses an On Error GoTo label action to handle any errors that might occur when opening a database connection:



On Error GoTo ErrorHandler Dim db As Database Set db = DBEngine.OpenDatabase("MyDB.mdb") 'Perform some database operations here db.Close Exit Sub ErrorHandler: MsgBox "An error occurred: " & Err.Description End Sub


The following code uses an On Error Resume Next action to handle any errors that might occur when looping through a recordset:



On Error Resume Next Dim rs As Recordset Set rs = db.OpenRecordset("Customers", dbOpenTable) Do While Not rs.EOF 'Perform some record operations here rs.MoveNext Loop


The following code uses an On Error GoTo 0 action to reset the error handler after handling an error:



On Error GoTo ErrorHandler Dim db As Database Set db = DBEngine.OpenDatabase("MyDB.mdb") 'Perform some database operations here db.Close Exit Sub ErrorHandler: MsgBox "An error occurred: " & Err.Description On Error GoTo 0 End Sub


How to Generate PDF Reports with DAO in VB 6.0




The final topic that we will cover in this article is how to generate PDF reports with DAO in VB 6.0. PDF stands for Portable Document Format, which is a file format that preserves the layout and appearance of documents across different platforms and devices.


PDF reports are useful when you want to create professional-looking documents that contain data from your databases, such as invoices, receipts, statements, charts, etc.


To generate PDF reports with DAO in VB 6.0, you need to use a third-party component called PDF Creator. PDF Creator is a free and open-source software that allows you to create PDF files from any Windows application that supports printing.


You can download PDF Creator from its official website: https://www.pdfforge.org/pdfcreator


After downloading and installing PDF Creator on your computer, you need to follow these steps to generate PDF reports with DAO in VB 6.0:


Install and Configure PDF Creator




After installing PDF Creator on your computer, you need to configure it properly for your VB project. Here are the steps you need to follow:


Add PDF Creator Reference to VB Project




After installing PDF Creator on your computer, you need to add a reference to it in your VB project. This will enable you to use the PDF Creator objects and methods in your code.


To add a PDF Creator reference, open your VB project and go to Project > References. In the References dialog box, scroll down and check the box next to "PDFCreator". Click OK to close the dialog box.


Set PDF Creator Properties and Options




After adding a PDF Creator reference, you need to set some properties and options for PDF Creator in your VB project. This will ensure that PDF Creator works correctly and efficiently in your project.


To set PDF Creator properties and options, you need to use the cOptions object. The cOptions object is a global object that provides access to the PDF Creator settings and features.


You can use the cOptions object to set various properties and options for P


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