DataTable Objects

The DataTable object is a core component of ADO.NET, representing an in-memory table of data. It is used to store and manipulate data retrieved from a data source, independent of the data source itself.

Key Features of DataTable

Schema Definition: A DataTable defines its schema through Columns and Constraints.
Data Storage: It stores data in rows, where each row contains values for the defined columns.
Data Manipulation: Supports adding, deleting, and modifying rows, as well as filtering and sorting data.
Relationships: Can participate in relationships with other DataTable objects within a DataSet.
Versioning: Supports row versioning (Current, Original, Proposed) for tracking changes.

Creating and Populating a DataTable

You can create a DataTable programmatically or have it created by a DataAdapter.

Here's a simple example of creating a DataTable and adding columns and rows:


                // C# Example
                DataTable productsTable = new DataTable("Products");

                // Define columns
                DataColumn idColumn = new DataColumn("ProductID", typeof(int));
                idColumn.AutoIncrement = true;
                idColumn.AutoIncrementSeed = 1;
                productsTable.Columns.Add(idColumn);

                DataColumn nameColumn = new DataColumn("ProductName", typeof(string));
                nameColumn.MaxLength = 50;
                productsTable.Columns.Add(nameColumn);

                DataColumn priceColumn = new DataColumn("Price", typeof(decimal));
                productsTable.Columns.Add(priceColumn);

                // Add constraints (optional)
                productsTable.Constraints.Add(new UniqueConstraint("PK_ProductID", idColumn));

                // Add rows
                DataRow row1 = productsTable.NewRow();
                row1["ProductName"] = "Laptop";
                row1["Price"] = 1200.50m;
                productsTable.Rows.Add(row1);

                DataRow row2 = productsTable.NewRow();
                row2["ProductName"] = "Keyboard";
                row2["Price"] = 75.00m;
                productsTable.Rows.Add(row2);

                // Access data
                foreach (DataRow row in productsTable.Rows)
                {
                    Console.WriteLine($"ID: {row["ProductID"]}, Name: {row["ProductName"]}, Price: {row["Price"]}");
                }

DataTable Schema Elements

Columns

DataColumn objects define the structure of the DataTable. Each column has a name, a data type, and can have properties like AllowDBNull, AutoIncrement, and MaxLength.

Constraints

Constraint objects enforce rules on the data within a DataTable. Common constraints include:

UniqueConstraint: Ensures that all values in a specified column or set of columns are unique.
ForeignKeyConstraint: Defines a relationship between two tables, ensuring referential integrity.

The DataTable provides a powerful abstraction for working with structured data in memory, making it a cornerstone for disconnected data access scenarios in ADO.NET.

Working with Rows

DataRow objects represent a single record within a DataTable. You can create new rows using NewRow() and add them to the table's Rows collection.

You can access, modify, and delete rows. When modifying a row, ADO.NET tracks the changes, allowing you to accept or reject them.

Filtering and Searching

DataTable offers efficient ways to find specific rows:

Select() method: Returns an array of DataRow objects that match a specified filter expression.
Find() method: Quickly finds a row based on its primary key values.

Example using Select():


                // Find products with price greater than 100
                DataRow[] expensiveProducts = productsTable.Select("Price > 100");
                foreach (DataRow row in expensiveProducts)
                {
                    Console.WriteLine($"Expensive Product: {row["ProductName"]}");
                }

DataTable and DataSet

A DataTable is often used within a DataSet. A DataSet can contain multiple DataTable objects, along with relationships between them, allowing you to model complex data structures.

Understanding DataTable is crucial for efficient data management in ADO.NET applications, especially when dealing with large amounts of data or disconnected architectures.