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Datasets in Microsoft.Net


ADO.NET was designed to meet the needs of a new programming model: disconnected data architecture, tight integration with XML, common data representation with the ability to combine data from multiple and varied data sources, and optimized facilities for interacting with a database, all native to the .NET Framework.The ADO.NET DataSet is a memory-resident representation of data that provides a consistent relational programming model regardless of the source of the data it contains.

Author Info:
By: Raghav Nayak
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March 24, 2004
TABLE OF CONTENTS:
  1. · Datasets in Microsoft.Net
  2. · RecordSet Objects
  3. · Validating data in DataSet
  4. · Validation Properties of the DataColumn
  5. · The DataTable Object’s Constraints Collection
  6. · Creating Dataset at Design Time
  7. · Adding DataColumn Objects
  8. · New DataSet

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Datasets in Microsoft.Net - The DataTable Object’s Constraints Collection
(Page 5 of 8 )

You can also validate data in your DataSet by setting properties of the DataTable object. The ADO.NET object model includes two classes that you can use to define constraints in a DataTable. These classes, UniqueConstraint and ForeignKeyConstraint, are derived from the Constraint class. The DataTable exposes a Constraints property that you can use to add to, modify, or examine the constraints on the DataTable.


  1. UniqueConstraints
    If you set the Unique property of a DataColumn to True, you’ve defined a unique constraint in the DataTable that contains that column. At the same time, you’ve also added a UniqueConstraint object to the DataTable object’s Constraints collection. Setting the Unique property of a DataColumn is simpler than creating a new UniqueConstraint in a DataTable object’s Constraints collection. However, there are times when you’ll want to explicitly create a UniqueConstraint, such as when you need to make sure that the combinations of values from multiple columns are unique.

  2. PrimaryKey
    A primary key is a special type of unique constraint. The ADO.NET DataRowCollection object has a Find method that you can use to locate a row in your DataTable by the value or values in its primary key column, as shown here.

    row MyTable.Rows.Find("RAGS")


    A DataTable can have multiple unique constraints but can contain at most one primary key. You can set or examine a DataTable object’s primary key using its PrimaryKey property.

  3. ForeignKeyConstraint
    You can also add foreign constraints to a DataTable. I described an example of a foreign key constraint just a couple pages back. Each order in the Northwind database’s Orders table must have a value for its CustomerID column that is used in the Customers table. You can place similar restrictions on the data in your DataSet by creating a ForeignKeyConstraint and adding it to the table whose rows you want to validate.

You generally won’t need to explicitly create a ForeignKeyConstraint. Creating a DataRelation between two DataTable objects within your DataSet creates a ForeignKeyConstraint in the process. In the next chapter, I’ll discuss the DataRelation object and how you can use it to work with relational data.


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