A DataTable is a powerful class in the System.Data namespace that can be used to store and manipulate tabular data in a C# program. It provides a convenient way to work with data in a structured way, and it offers a variety of methods and properties for performing common data operations.
To create a DataTable, you can use the following code:
1 2 3 | DataTable table = new DataTable(); |
This creates an empty DataTable object. You can then add columns to the DataTable by using the Columns property:
1 2 3 4 | table.Columns.Add("Name", typeof(string)); table.Columns.Add("Age", typeof(int)); |
This adds two columns to the DataTable: one for a person’s name and one for their age. The Add method takes two arguments: the name of the column and the data type of the column.
You can add rows to the DataTable by using the Rows property:
1 2 3 4 5 | table.Rows.Add("Alice", 25); table.Rows.Add("Bob", 30); table.Rows.Add("Eve", 28); |
This adds three rows to the DataTable, each representing a person with a name and an age.
You can access the data in the DataTable using the Rows property and the ItemArray property of the DataRow class:
1 2 3 4 5 6 | foreach (DataRow row in table.Rows) { Console.WriteLine("Name: {0}, Age: {1}", row["Name"], row["Age"]); } |
This code iterates through the rows of the DataTable and prints the name and age for each person.
The DataTable class also provides a variety of methods and properties for sorting, filtering, and searching data, as well as for converting the data to other formats such as XML and JSON. It is a useful tool for working with data in a C# program, and it is often used in conjunction with a DataAdapter and a DataSet to read and write data from a database.
In addition to the methods and properties mentioned above, the DataTable class provides several other useful features for working with data. Here are a few examples:
Sorting data
To sort the data in a DataTable, you can use the DefaultView property and the Sort method:
1 2 3 | table.DefaultView.Sort = "Name ASC"; |
This sorts the data in the DataTable by the Name column in ascending order. You can use the DESC keyword to sort in descending order.
Filtering data
To filter the data in a DataTable, you can use the DefaultView property and the RowFilter property:
1 2 3 | table.DefaultView.RowFilter = "Age > 25"; |
This filters the data to show only rows where the Age column is greater than 25.
Searching for data
To search for data in a DataTable, you can use the Select method and a filter expression:
1 2 3 | DataRow[] rows = table.Select("Name='Bob'"); |
This searches the DataTable for rows where the Name column is equal to “Bob” and returns an array of DataRow objects that match the search criteria.
Converting data to other formats
To convert the data in a DataTable to another format, such as XML or JSON, you can use the WriteXml and WriteXmlSchema methods to generate an XML representation of the data, or the ToJson method to generate a JSON representation of the data:
1 2 3 4 | string xml = table.WriteXml(); string json = table.ToJson(); |
The WriteXml method generates an XML representation of the data in the DataTable, including the schema (structure) of the table and the data itself. The WriteXmlSchema method generates only the schema of the table. The ToJson method generates a JSON representation of the data in the DataTable.
Working with a database
The DataTable class can be used in conjunction with a DataAdapter and a DataSet to read and write data from a database. A DataAdapter is a class that retrieves data from a database and stores it in a DataSet, and a DataSet is an in-memory cache of data that can be used to store and manipulate data from a database or other data source.
To populate a DataTable with data from a database, you can use the Fill method of a DataAdapter:
1 2 3 4 5 6 7 8 9 10 | string connectionString = "..."; string queryString = "SELECT * FROM Customers"; using (SqlConnection connection = new SqlConnection(connectionString)) { SqlDataAdapter adapter = new SqlDataAdapter(queryString, connection); adapter.Fill(table); } |
This code creates a SqlDataAdapter object and uses it to execute a SQL query that retrieves all rows from the Customers table. It then uses the Fill method to populate the DataTable with the data from the database.
To update the data in a database with the data in a DataTable, you can use the Update method of the DataAdapter:
1 2 3 4 5 6 7 8 9 10 | string connectionString = "..."; using (SqlConnection connection = new SqlConnection(connectionString)) { SqlDataAdapter adapter = new SqlDataAdapter("SELECT * FROM Customers", connection); SqlCommandBuilder builder = new SqlCommandBuilder(adapter); adapter.Update(table); } |
This code creates a SqlDataAdapter object and a SqlCommandBuilder object, and uses them to update the data in the database with the data in the DataTable.
These are just a few examples of how to use the DataTable class to work with data in a C# program. The DataTable class is a powerful and versatile tool that can be used in many different contexts to store and manipulate data.
Here are a few more tips for working with DataTable objects:
Accessing data by column name or index
You can access the data in a DataTable by either the column name or the column index. For example, the following code accesses the value of the Age column in the first row of the DataTable using both the column name and the column index:
1 2 3 4 | int age1 = (int)table.Rows[0]["Age"]; int age2 = (int)table.Rows[0][1]; |
Modifying data in a DataTable
You can modify the data in a DataTable by using the ItemArray property of the DataRow class. For example, the following code sets the Name and Age columns of the first row of the DataTable to new values:
1 2 3 4 | table.Rows[0]["Name"] = "Charlie"; table.Rows[0]["Age"] = 35; |
You can also use the SetField method to set the value of a specific column in a DataRow:
1 2 3 4 | row.SetField("Name", "Charlie"); row.SetField("Age", 35); |
