vb.net qr code sample s INTRODUCING DATASETS AND DATA ADAPTERS in VB.NET

Generation DataMatrix in VB.NET s INTRODUCING DATASETS AND DATA ADAPTERS

CHAPTER 8 s INTRODUCING DATASETS AND DATA ADAPTERS
Print Data Matrix ECC200 In Visual Basic .NET
Using Barcode generator for Visual Studio .NET Control to generate, create Data Matrix image in .NET framework applications.
www.OnBarcode.com
Data Matrix ECC200 Decoder In Visual Basic .NET
Using Barcode decoder for Visual Studio .NET Control to read, scan read, scan image in Visual Studio .NET applications.
www.OnBarcode.com
Let s look at an example. Imagine you re trying to connect to a remote database server over the Internet for detailed information about some business transactions. You search on a particular date for all available transactions, and the results are displayed. Behind the scenes, your application creates a connection with the data source, joins a couple of tables, and retrieves the results. Suppose you now want to edit this information and add or remove details. Whatever the reason, your application will go through the same cycle over and over again: creating a new connection, joining tables, and retrieving data. Not only is there overhead in creating a new connection each time, but you may be doing a lot of other redundant work, especially if you re dealing with the same data. Wouldn t it be better if you could connect to the data source once, store the data locally in a structure that resembles a relational database, close the connection, modify the local data, and then propagate the changes to the data source when the time is right This is exactly what the dataset is designed to do. A dataset stores relational data as collections of data tables. You met data tables briefly in the previous chapter when a System.Data.DataTable object was to hold schema information. In that instance, however, the data table contained only schema information, but in a dataset, the data tables contain both metadata describing the structure of the data and the data itself. Figure 8-1 shows the dataset architecture.
Barcode Generator In VB.NET
Using Barcode generator for .NET framework Control to generate, create Barcode image in .NET framework applications.
www.OnBarcode.com
Paint ANSI/AIM Code 39 In Visual Basic .NET
Using Barcode drawer for .NET Control to generate, create Code39 image in .NET applications.
www.OnBarcode.com
Figure 8-1. Dataset architecture
QR Code ISO/IEC18004 Generation In Visual Basic .NET
Using Barcode generator for VS .NET Control to generate, create QR-Code image in .NET framework applications.
www.OnBarcode.com
PDF417 Creator In Visual Basic .NET
Using Barcode generator for .NET Control to generate, create PDF-417 2d barcode image in VS .NET applications.
www.OnBarcode.com
CHAPTER 8 s INTRODUCING DATASETS AND DATA ADAPTERS
Paint Matrix In Visual Basic .NET
Using Barcode generator for .NET Control to generate, create Matrix 2D Barcode image in .NET framework applications.
www.OnBarcode.com
Make 2 Of 5 Interleaved In VB.NET
Using Barcode printer for .NET framework Control to generate, create I-2/5 image in Visual Studio .NET applications.
www.OnBarcode.com
The architecture mirrors the logical design of a relational database. You ll see how to use data tables, data rows, and data columns in this chapter, but we won t cover constraints and will leave relationships until 11.
Creating Data Matrix 2d Barcode In Objective-C
Using Barcode creation for iPhone Control to generate, create DataMatrix image in iPhone applications.
www.OnBarcode.com
DataMatrix Recognizer In Visual Studio .NET
Using Barcode decoder for .NET Control to read, scan read, scan image in Visual Studio .NET applications.
www.OnBarcode.com
A Brief Introduction to Data Adapters
Print EAN / UCC - 13 In .NET
Using Barcode generation for ASP.NET Control to generate, create GS1 - 13 image in ASP.NET applications.
www.OnBarcode.com
USS Code 39 Generator In None
Using Barcode creator for Online Control to generate, create Code 39 Full ASCII image in Online applications.
www.OnBarcode.com
When you first instantiate a dataset, it contains no data. You obtain a populated dataset by passing it to a data adapter, which takes care of connection details and is a component of a data provider. A dataset isn t part of a data provider. It s like a bucket, ready to be filled with water, but it needs an external pipe to let the water in. In other words, the dataset needs a data adapter to populate it with data and to support access to the data source. Each data provider has its own data adapter in the same way that it has its own connection, command, and data reader. Figure 8-2 depicts the interactions between the dataset, data adapter, and data source.
UCC.EAN - 128 Creator In None
Using Barcode encoder for Microsoft Excel Control to generate, create GS1 128 image in Office Excel applications.
www.OnBarcode.com
Barcode Drawer In Objective-C
Using Barcode printer for iPhone Control to generate, create Barcode image in iPhone applications.
www.OnBarcode.com
Figure 8-2. Dataset, data adapter, and data source interaction
Create Barcode In Visual Studio .NET
Using Barcode creation for Reporting Service Control to generate, create Barcode image in Reporting Service applications.
www.OnBarcode.com
UPC - 13 Maker In None
Using Barcode printer for Font Control to generate, create GTIN - 13 image in Font applications.
www.OnBarcode.com
The data adapter constructor is overloaded. You can use any of the following to get a new data adapter. We re using the SQL Server data provider, but the constructors for the other data providers are analogous.
Reading UCC - 12 In VB.NET
Using Barcode recognizer for .NET framework Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
Generating QR-Code In Java
Using Barcode creation for Eclipse BIRT Control to generate, create QR Code image in BIRT applications.
www.OnBarcode.com
Dim Dim Dim Dim da da da da as as as as SqlDataAdapter SqlDataAdapter SqlDataAdapter SqlDataAdapter = = = = new new new new SqlDataAdapter() SqlDataAdapter(cmd) SqlDataAdapter(sql, conn) SqlDataAdapter(sql, connString)
Generate GTIN - 128 In None
Using Barcode generation for Font Control to generate, create GTIN - 128 image in Font applications.
www.OnBarcode.com
EAN / UCC - 13 Encoder In Objective-C
Using Barcode creator for iPad Control to generate, create EAN 128 image in iPad applications.
www.OnBarcode.com
CHAPTER 8 s INTRODUCING DATASETS AND DATA ADAPTERS
So, you can create a data adapter in four ways: You can use its parameterless constructor (assigning SQL and the connection later). You can pass its constructor a command (here, cmd is a SqlCommand object). You can pass a SQL string and a connection. You can pass a SQL string and a connection string. You ll see all this working in action shortly. For now, we ll move on and show how to use data tables, data columns, and data rows. You ll use these in upcoming sections.
A Brief Introduction to Data Tables, Data Columns, and Data Rows
A data table is an instance of the class System.Data.DataTable. It s conceptually analogous to a relational table. As shown in Figure 8-1, a data table has collections of data rows and data columns. You can access these nested collections via the Rows and Columns properties of the data table. A data table can represent a stand-alone independent table, either inside a dataset as you ll see in this chapter or as an object created by another method, as you saw in the previous chapter when a data table was returned by calling the GetSchemaTable method on a data reader. A data column represents the schema of a column within a data table and can then be used to set or get column properties. For example, you could use it to set the default value of a column by assigning a value to the DefaultValue property of the data column. You obtain the collection of data columns using the data table s Columns property, whose indexer accepts either a column name or a zero-based index, for example (where dt is a data table):
Dim col as DataColumn = dt.Columns("ContactName") Dim col as DataColumn = dt.Columns(2)
A data row represents the data in a row. You can programmatically add, update, or delete rows in a data table. To access rows in a data table, you use its Rows property, whose indexer accepts a zero-based index, for example (where dt is a data table):
Dim row as DataRow = dt.Rows(2)
That s enough theory for now. It s time to do some coding and see how these objects work together in practice!
Copyright © OnBarcode.com . All rights reserved.