Using DataSet, DataView, and DataViewManager

This article has been excerpted from the book "A Programmer's Guide to ADO.NET in C#". ADO.NET provides components to view data in data bound controls. These components are easy to use and provide rapid development. You just drag and drop these controls to a form, set their properties, and bind them to Data- bound controls. Then you're all set to run your programs. The DataView and DataViewManager classes fall in this category. You can use these classes to represent different views of a data table based on different filter and sort criterion. You can use these classes either at design-time or run-time modes. Earlier, you've seen how use these class either at design-time modes. You've also seen how to use class objects at design-time. In this article, you'll see how to use these classes programmatically. A DataSet is a key component in the ADO.NET data model. It's an in-memory representation of one or multiple data tables, relations, and constraints. It provides a communication between the actual data Windows forms and Web Forms controls to provide the data a view through the DataView and the DataViewManager. Not only this, but a DataSet offers much more than that. The DataView is useful when you need to bind a DataTable or multiple DataTable objects with data-bound controls. You can also represent multiple views of same data by applying a filter and sort on a data table, and you can bind these multiple views to different data-bound controls such as a DataGrid, DataList, comboBox, and ListBox control. Figure 1 shows the relationship between a DataSet, DataTable, DataView, and Windows and Web Forms controls. As you can see from figure 1, a Data Set contains and Web Forms controls. As you can see from figure 1, a DataSet contains three DataTable objects, which are represented by three different views. The three different DataView objects bind to different data bound controls. Figure 1: Relation ship between the DataSet, DataTable, and DataView

The DataSet

A DataSet object plays a vital role in the ADO.NET component model. A DataSet represents disconnected cache of Data in the form of tables, rows, columns, or XML schemas. If you've ever programmed a database application in previous versions of Visual studio, you're probably familiar with recordset. A recordset object was a way to represent data in your programs. Similar to a recordset, a DataSet represent data in your applications. Once you have constructed a DataSet, you can get or set data in your Applications or your data source. As mentioned earlier, the DataSet works in both connected and disconnected environment. A DataSet communicates with a DataAdapter and calls DataAdapter's Fill method to fill data from a DataAdapters. You can fill a DataSet object with multiple tables or stored from a DataAdapter. In this article, you'll see how it works with DataTable and DataView objects. As you can see in figure 2, the Fill method of data adapter fills data from a data adapter to a dataset. Once data is filled to a DataSet from a DataAdapter, you can view it in Windows or Web applications by binding data to data-bound through a DataView. You can generate one or multiple views for a data tables based on the filter and sort criteria. Figure 2: The relationship between DataSet, DataAdapter, and DataView objects The DataSet class represents a dataset in ADO.NET. As you've seen earlier, a DataSet can have multiple DataTable objects. The DataTableCollection object represents all DataSet objects related to DataSet. The Tables property of the Dataset represents the collection of DataTable objects. The tables relate to each other with DataRelation objects, discussed earlier in this article. The DataRelationCollection represents all available relations in the DataSet. The Relations property represents the DataRelationCollection of DataSet. Table 1 describes some DataSet properties. A DataSet object stores data in XML format. An XML schema represents a dataset. A DataSet also defines methods to read and write XML documents. The ReadXml method reads an XML document and fills the DataSet with the XML data and the WriteXML method writes DataSet data to an XML document. This class also defines the methods ReadXMLSchema and WriteXMLSchema to read and write XML schema. Table 2 describes some of the DataSet class members. I'll use these methods and properties through out this article's examples. Table 1: The DataSet Class Properties

PROPERTY	DESCRIPTION
DataSetName	Represent the name of the Dataset
DefaultViewManager	Default view of the data of a DataSet
Relations	Collection of relations of a DataSet that links multiple tables
Tables	Collection of tables contained in a DataSet

Table 2: The Data Set Class Methods

METHOD	DESCRIPTION
AcceptChanges	Commits all the changes made since last AcceptChanges called
BeginInit	Begins initialization if a DataSet was used previously
Clear	Removes all data from a DataSet
Clone	Clones the structure of a DataSet
Copy	Copies a dataset's data and structure
EndInit	Ends the initialization
GetChanges	Gets a copy of dataset containing all changes made since last AcceptChanges was called or loaded
GetXml	Returns the XML representation of the data stored in a DataSet
GetXmlSchema	Returns XML schema of the data stored in a DataSet
Merge	Merges two DataSet objects
ReadXmlSchema	Reads an XML schema and fills data in a DataSet
RejectChanges	Rejects all changes made to the DataSet since it was created or AcceptChanges called
Reset	Reset a DataSet to its original state
WriteXml	Write data of a DataSet to an XML document
WriteXmlSchema	Write data of a DataSet to an XML schema

Typed and Untyped DataSets

There are two kinds of DataSet: typed or untyped. A typed DataSet first comes from the DataSet class and then uses XML schema (.xsd file) to generate a new class. You've seen how to create a typed dataset using VS.NET earlier. An untyped dataset has no build-in schema. You create an instance of DataSet class and call its methods and properties to work with the Data Source. All elements of an untyped dataset are collections. In this article, you'll work with untyped datasets. Both kinds of dataset have their own advantages and disadvantages. Typed datasets take less time to write applications but offer no flexibility. They're useful when you already know the schema of a database. The biggest advantage of typed datasets is the VS.NET IDE support you can drag a database table, its columns or stored procedures to a form in your application and the IDE generates typed dataset for you. After that you can bind these datasets to the controls. There are many occasions when you don't know the schema of a database. In those cases, the untyped datasets are useful. The untyped datasets also provide the flexibility of connecting with multiple data source. And you can use them without the VS. NET IDE.

The DataView

Another powerful feature of ADO.NET is the ability to create several different views of the same data. You can sort these views differently and filter them on different criteria. They can contain different row state information. As you've seen in figure 5-18, a DataView represents a customized view of data table and can bind to windows Forms and Web Forms controls. Using DataView sort and filter features, you can also have multiple views of a single data table. Using RowFilter and Sort properties, you can apply a filter on a DataView and sort its contents before binding it to a data-bound control. The AddNew method adds a new row to a Dataview, and the Delete method deletes a row from a DataView. You can use the Find and FindRows methods to search for rows based on the defined criteria. Table 3 describes some of the DataView properties, and Table 4 describes some of its methods. Table 3: The DataView Class properties

PROPERTIES	DESCRIPTION
AllowDelete	Indicates weather deletes are allowed
AllowEdit	Indicates whether edits are allowed
AddNews	Indicates whether new rows can be added
Count	Represents the number of records in a DataView after RowFilter and RowstateFilter have been applied
DataViewManager	DataViewManager associates with this view
Item	Represent an item of a row
RowFilter	Represent the expression used to filter rows to view in the DataView
Sort	Represent the sort column and sort order
Table	DataTable attached with this view

Table 4: The DataView Class Methods

METHOD	DESCRIPTION
AddNew	Add a new row to the DataView
BeginInit	Begins the initialization if a data view was previously used
Delete	Deletes a row
Find	Finds a row in the DataView based on the specified criteria
FindRows	Returns an array of rows based on the specified criteria

The DataView Manager

A DataViewManager contains a collection of views of a dataset, one view for each data table in the dataset. The DataViewManager has a DataViewSettings property that enables the user to construct a different view for each data table in the dataset. If you want to create two views on the same data table, you need to create another instance of the DataViewManager and construct the DataViewSetting for that particular view. Then you construct a DataView using the DataViewManager. For example, in the Orders DataSet, you may want to filter out the orders with an EmployeedId of 4 and sort the orders by the date they were shipped. You can retrieve records using the sort and filter properties of the DataSet and attach the filtered and sorted data to DataView or a DataViewManager. To construct a Data View Manager you can either use the Default constructor or pass in a DataSet object. For example: Or The DataViewManager has a few properties you need to know about to utilize it effectively. Table 5 shows the main properties. Table 5: Data Set View properties

PROPERTY	DESCRIPTION
DataSet	The DataSet being viewed of type DataSet
DataViewSettings	Contains the collection of TableSetting object for each table in the DataSet. The Table Setting object contains the sorting and filtering criteria for a particular table.

The DataViewManager contains the CreateDataView method allows you to create a DataView object for a particular table in your DataSet. You can construct the DataView for the table with the DataViewManager's DataViewSetting for the particular DataTable of the DataSet. You can also adjust settings for the DataView by assigning filter and sort properties directly in the DataView.

Conclusion

Hope this article would have helped you in understanding the DataSet, DataView and DataViewManager, Typed and Untyped DataSets in ADO.NET. See my other articles on the website on ADO.NET.