Tutorials – ADO.Net

DataViews in ADO.NET provide a flexible and powerful way to filter, sort, and navigate through data within DataTables or DataSets. This chapter explores the significance of DataViews, how to create and manipulate them, and their role in data presentation and interaction.

Understanding DataViews

A DataView is a customized view of a DataTable, which acts as a filter, sorter, and navigator for the data contained in the table. It allows you to present data in various ways without altering the underlying data structure. DataViews offer several key features and use cases:

1. Data Filtering: You can filter data in a DataView based on specific criteria, displaying only rows that meet certain conditions. This is valuable for showing subsets of data.
2. Data Sorting: DataViews allow you to sort data according to one or more columns in ascending or descending order. Sorting is useful for presenting data in a specific sequence.
3. Data Navigation: DataViews enable easy navigation through data, making it simple to move between records. This is beneficial when presenting data in a paginated or interactive manner.
4. Data Binding: DataViews are often used in data binding scenarios where they serve as the data source for various UI controls, such as grids and lists.
5. Data Aggregation: You can use DataViews for aggregation purposes, such as calculating totals or averages within a filtered set of data.

Creating DataViews

To create a DataView, you first need a DataTable as the source. Here’s how to create a DataView:

// Assuming you have a DataTable named "dataTable"
DataView dataView = new DataView(dataTable);

Once you have a DataView, you can manipulate it to filter, sort, or navigate the data as needed.

Filtering Data with DataViews

Filtering data using a DataView involves specifying a filter expression that determines which rows should be included. The filter expression is a string that resembles a SQL WHERE clause. For example:

dataView.RowFilter = "Category = 'Electronics' AND Price > 500";

The filter expression can include various comparison operators, logical operators, and functions, allowing for complex filtering conditions. For example:

dataView.RowFilter = "LastName LIKE 'S%' OR FirstName LIKE 'J%'";

Sorting Data with DataViews

Sorting data using a DataView is straightforward. You can specify one or more columns by which the data should be sorted, along with the sort direction (ascending or descending). For example:

dataView.Sort = "LastName ASC, FirstName DESC";

This will sort the data first by the “LastName” column in ascending order and then by the “FirstName” column in descending order.

Navigating Data with DataViews

DataViews provide methods for navigation, making it easy to move between records. Some useful methods include:

• dataView.MoveFirst(): Moves to the first row.
• dataView.MoveLast(): Moves to the last row.
• dataView.MoveNext(): Moves to the next row.
• dataView.MovePrevious(): Moves to the previous row.

These methods simplify the navigation through the filtered and sorted data set.

Binding DataViews to UI Controls

DataViews are often used as data sources for UI controls in data-driven applications. Popular UI controls like DataGridView in Windows Forms or GridView in ASP.NET can be bound to DataViews. For example, to bind a DataGridView in Windows Forms:

dataGridView.DataSource = dataView;

Similarly, in ASP.NET, you can bind a GridView to a DataView using markup or code-behind:

<asp:GridView ID="gridView1" runat="server"></asp:GridView>

gridView1.DataSource = dataView;
gridView1.DataBind();

Binding to DataViews simplifies the presentation of filtered and sorted data and ensures that any changes made to the DataView are automatically reflected in the UI control.

Data Aggregation with DataViews

DataViews can be used for data aggregation purposes, such as calculating sums, averages, counts, or other statistical measures on filtered data. Here’s an example of how to calculate the sum of a column using a DataView:

double sum = Convert.ToDouble(dataView.ToTable().Compute(“SUM(Price)”, “”));

This code first converts the DataView into a new DataTable (dataView.ToTable()) and then uses the Compute method to calculate the sum of the “Price” column for all filtered rows.

Best Practices for Working with DataViews

To make the most of DataViews in ADO.NET, consider these best practices:

1. Efficient Data Retrieval: If you’re working with large datasets, retrieve only the necessary data and apply filtering and sorting as late as possible in the process to reduce data transfer.
2. Encapsulate Logic: Consider encapsulating the logic for creating and manipulating DataViews within dedicated data access or business logic components. This promotes code reuse and maintainability.
3. Parameterized Filters: When using filter expressions, parameterize them to prevent SQL injection and improve performance. Avoid concatenating user input directly into filter expressions.
4. Indexing: If you anticipate frequent filtering or sorting of data, consider indexing the relevant columns in your DataTable, as this can significantly improve DataView performance.
5. Data Binding: When binding DataViews to UI controls, ensure that the DataView’s structure matches the expected structure of the UI control. Verify column names and data types to avoid runtime errors.
6. Testing: Test DataViews thoroughly, especially when implementing complex filter and sort expressions. Ensure that the DataView behaves as expected and that data is presented accurately.

Conclusion

DataViews in ADO.NET are a versatile tool for filtering, sorting, and navigating data within DataTables or DataSets. They provide a powerful way to present data in a customized manner without modifying the underlying data source. By understanding how to create and manipulate DataViews and by adhering to best practices, you can enhance the presentation and interaction of data in your data-driven applications. In the subsequent chapters, we will explore advanced topics in ADO.NET, including data relationships, data constraints, and data synchronization.