1. ADO.NET Framework

2. Lecture Overview Creating connections to providing
Executing SQL commands using providers that
Return nothing
Return one value
Read data one record at a time
Use DataAdapters to create in-memory datasets and datatables

3. Providers
Remember that ADO has different providers for each type of database
Each provider contains the same full set of classes and objects to work with the underlying DB
OleDb (System.Data.OleDb)
Oracle (System.Data.OracleClient)
SQL Server (System.Data.SqlCleint)

4. Connections (Introduction)
The OleDbConnection and SQLConnection classes give us the means to make a database connection
Commands are sent over this connection
The ConnectionString property contains the string that the systems uses to make the database connection
It differs from provider to provider

5. Connections (Using)
Call the Open and Close methods to explicitly open and close the connections
Use for OleDbCommands
Some objects call these methods for you

6. Connection (Example)

7. Using a Connection (Introduction)
Once we have created a connection, we send commands over that connection
Most commonly using the OleDbCommand or SqlCommand objects
There are properties to configure the command and connection
There are methods to execute the command using the connection

8. OleDbCommand (Properties)
CommandText property stores SQL statement that will be executed against a provider
Connection property stores a reference to existing OleDbConnection object
Parameters property stores a reference to a Parameters collection (more later)

9. OleDbCommand (Methods)
ExecuteScalar method executes a SELECT statement
Method returns the first column of the first row retrieved by the SELECT statement
Additional data is discarded and no exception will occur
ExecuteNonQuery method executes an SQL statement
Statement does not return database rows
ExecuteReader method creates a DataReader
We will go through each one of these next

10. Using the OleDbCommand Object (ExecuteScalar)
The ExecuteScalar method returns a single value (first column / first row)
Will not fail if you return multiple rows
Use to get a max ID value

11. ExecuteScalar (Example)

12. Using the OleDbCommand Object (ExecuteNonQuery)
Use to execute INSERT, UPDATE, or DELETE commands that do not return rows

13. The DataReader (Introduction)
It’s a forward-only reader (like a stream)
You read one record at a time
Each time a record is read, the reader contains a reference to an array of fields

14. Using the OleDbDataReader
Place an SQL SELECT statement in the OleDbcommand
Call ExecuteReader to create the forward-only reader
Call Read to read each record
Then call the various Get methods to get the value of each field

15. The DataReader (Example)

16. Returning a DataSet This gets a bit more complicated
We need another object called a DataAdapter
Microsoft calls it a bridge between a DataSet and a DataSource
Again, there are OleDb and Sql Server versions of these
I’ll go through the OleDbDataAdapter and DataSet, in turn

17. OleDbDataAdapter Class (Introduction)
OleDbDataAdapter works in conjunction with the DataSet class to read and write data
Commands are sent over a connection
Data is retrieved into a DataSet
Commands to insert, update, or delete data return nothing

18. OleDbDataAdapter (Properties)
SelectCommand property stores SQL SELECT statement
InsertCommand property stores SQL INSERT statement that will insert a row into a database table
UpdateCommand property stores a SQL UPDATE statement to update the contents of an existing row
DeleteCommand property stores a SQL DELETE statement that will remove a row or rows

19. OleDbDataAdapter (Methods)
Fill method uses an OleDbConnection to retrieve database records
Records are loaded into a DataSet
Update method examines the DataSet for any added, changed, or deleted records
Changes are recorded to DataSet
Call AcceptChanges method on DataSet to synchronize DataSet and database

20. OleDbDataAdapter (Events)
FillError event fires if an error occurs while populating the DataSet
RowUpdating event fires just before row is updated
RowUpdated event fires just after a row in the data source is updated

21. OleDbDataAdapter Class

22. Filling the OleDbDataAdapter (1)

23. Definition (DataSet)
It’s an in-memory representation of one or more tables in a database
It’s created by a data adapter
It can be accessed programmatically
It contains one or more DataTable objects

24. DataSet Properties
Boolean CaseSensitive property controls whether String comparisons are made in a case sensitive or case insensitive way
DataSetName property defines the name of the DataSet
EnforceConstraints property defines whether ADO.NET checks constraint rules when adding, changing, or deleting data
Tables property returns the collection of DataTable objects in the DataSet

25. DataSet Methods (1)
AcceptChanges method causes any changed records to be marked as unchanged records
Use to synchronize database with DataSet
Clear method removes all rows from all tables in the DataSet
Clone method makes a copy of the DataSet schema (structure)
Data is not copied
Copy method copies both the schema and the data from a DataSet
Creates an exact copy of the original DataSet

26. DataSet Methods (2)
GetChanges method (overloaded) examines an existing DataSet and returns a new DataSet containing only the changed records
Returns null if DataSet does not contain changes
HasChanges method returns a Boolean value indicating whether the DataSet has pending changes
RejectChanges method causes any pending changes to be cancelled, restoring any data to their original values

27. DataTable Class (Introduction)
A DataSet object typically contains one or more DataTable objects
It’s basically a database table
DataTable object contains one or more DataColumn objects representing each column

28. DataTable (Properties)
CaseSensitive property of the DataTable has the same value as the CaseSensitive property of the parent DataSet
Columns property contains a reference to a DataColumnCollection
Use to reference each column
HasErrors property (Boolean) is set to True if any of the rows contain errors
PrimaryKey property contains an array of DataColumn objects
Rows property is a collection having a data type of DataRowCollection

29. DataRow Class
Each row in the Rows collection has a data type of DataRow
Item property gets or sets the value for a particular column in a DataRow
Item property accepts one argument
RowState property indicates whether the DataRow is a new row, a deleted row, or a row whose contents have been modified
Delete method of the DataRow class marks the row for deletion
Row is not deleted until the AcceptChanges method of the DataSet or DataTable is called

30. DataTable and Rows Relationship