ADO.NET Dataset Structure - MSDN Documentation

Dataset Structure

The DataSet object is a core component of ADO.NET, providing an in-memory representation of data. It can hold multiple tables, relationships, and constraints, allowing you to work with data independently of the data source.

Key Components of a DataSet

A DataSet is composed of several key elements that define its structure and content:

Tables: DataTable objects represent the individual tables within the DataSet. Each DataTable contains rows and columns.
Relations: DataRelation objects define relationships between tables, similar to foreign key relationships in a relational database.
Constraints: Constraint objects enforce data integrity rules, such as unique values (UniqueConstraint) and referential integrity (ForeignKeyConstraint).

DataTable Object

The DataTable object is the building block for representing tabular data within a DataSet. It has the following important members:

Columns

The Columns collection of a DataTable defines the schema of the table, including column names, data types, and nullability.


                        public DataColumnCollection Columns { get; }

Rows

The Rows collection holds the actual data as DataRow objects. You can add, delete, and modify rows within this collection.


                        public DataRowCollection Rows { get; }

Primary Key

You can define a primary key for a DataTable to uniquely identify rows.


                        public DataColumn[] PrimaryKey { get; set; }

Example: Creating a DataSet with Tables

Here's a simple example demonstrating how to create a DataSet and add a DataTable to it:

                    
                        // Create a new DataSet
                        DataSet myDataSet = new DataSet("CompanyData");

                        // Create a DataTable for Employees
                        DataTable employeesTable = new DataTable("Employees");

                        // Define columns for the Employees table
                        DataColumn employeeIdColumn = new DataColumn("EmployeeID", typeof(int));
                        employeeIdColumn.AutoIncrement = true;
                        employeeIdColumn.AutoIncrementSeed = 1;
                        employeeIdColumn.AutoIncrementStep = 1;
                        employeeIdColumn.AllowDBNulls = false;

                        DataColumn firstNameColumn = new DataColumn("FirstName", typeof(string));
                        DataColumn lastNameColumn = new DataColumn("LastName", typeof(string));

                        // Add columns to the table
                        employeesTable.Columns.Add(employeeIdColumn);
                        employeesTable.Columns.Add(firstNameColumn);
                        employeesTable.Columns.Add(lastNameColumn);

                        // Set the primary key
                        employeesTable.PrimaryKey = new DataColumn[] { employeeIdColumn };

                        // Add the DataTable to the DataSet
                        myDataSet.Tables.Add(employeesTable);

                        // Now you can add rows to the employeesTable...
                    
                

Relationships and Constraints

DataRelation objects are crucial for defining how tables are linked. This allows you to navigate from a parent row to child rows and vice-versa.

Constraint objects, such as UniqueConstraint and ForeignKeyConstraint, are essential for maintaining data integrity within the DataSet.

Note: A DataSet provides a rich set of features for managing data in memory, including sorting, filtering, searching, and data validation.

Summary

Understanding the structure of a DataSet, including its DataTable, DataColumn, and DataRow components, is fundamental to effectively using ADO.NET for data manipulation in your .NET applications.