Download Active Data Objects in .Net

Active Data Objects
Binding ASP.NET Controls to Data
Jim Fawcett
CSE686 – Internet Programming
Summer 2004
Support for Data in .Net
• Connected data access:
– Use Connection object and Command to connect a DataReader
object to database and read iteratively.
– Use Connection object and Command to connect a DataReader
and execute an SQL statement or stored procedure.
• Disconnected data access:
– Use a Connection and Command to connect a DataAdapter to the
database and fill a DataSet with the results.
– Use a Connection and Command to connect a DataAdaptor to the
database and then call Update method of the DataSet.
Data Provider Classes
OleDbConnection
OleDbCommand
OleDbDataReader
SqlConnection
OleDbDataAdapter
SqlDataAdapter
DataSet
SqlCommand
SqlDataReader
ADO Objects
DataAdapter
SelectCommand
Command
Connection
UpdateCommand
Connection
CommandText
ConnectionString
InsertCommand
CommandType
DeleteCommand
DataTable
DataSet
Rows Collection
Tables Collection
Columns Collection
Relations Collection
database
Constraints Collection
DataGrid
ChildRelations
Collection
ParentRelations
Collection
Connection Object
• Methods
– Open()
– Close()
– BeginTransaction()
• Properties
– ConnectionString
• "server=HINDENBURG\\NETSDK;Integrated Security=SSPI; database=pubs"
Command Object
•
•
Used to connect Connection Object to DataReader or a DataAdapter object
and execute commands.
Methods
– ExecuteNonQuery()
• Executes command defined in CommandText property, e.g., UPDATE, DELETE, INSERT,
CREATE TABLE, ALTER COLUMN, …
• Used for operations that do not return a row of data
– ExecuteReader(CommandBehavior)
• Returns a DataReader instance attached to the resulting rowset
• Assumes you’ve defined a command that implies a query, using CommandText property
– ExecuteScalar()
• Executes query defined in CommandText and returns the first column of the first row of
resulting rowset. Ignores the rest.
•
Properties
– Connection
– CommandText
– CommandType
connection string defining Server and database
Text of SQL query
StoredProcedure | TableDirect | Text (SQL Query)
DataReader Object
• Supports one-way, forward-only, access to data
• Methods
– Read()
• Returns one row and advances current row pointer
– GetBoolean, GetInt16, GetChars, GetString, GetValue
– Close()
• Properties
– this[string]
– this[int]
• Normally, a DataReader is returned from a command
object, ready to bind to a display control. You get one
from the command method ExecuteReader().
Data Adapter Object
• Used to:
– extract data from data source and populate tables in a DataSet
– Push changes in DataSet back to source
• Methods
– Fill(DataSet, Table)
– FillSchema(DataSet, SchemaType)
– Update()
• Properties
–
–
–
–
SelectCommand
UpdateCommand
InsertCommand
DeleteCommand
DataSet Object
• Used for Disconnected manipulation of a source’s data.
• Methods
–
–
–
–
–
–
Clear()
ReadXML(XmlReader)
WriteXML(XmlWriter)
AcceptChanges()
HasChanges()
AbandonChanges()
• Properties
– Tables collection
• ds.Tables[tableStr].Rows[3]["Responsible Individual"] = userID;
– Relations collection
• Normally, you don’t fill the DataSet, a DataAdapter does that.
Managing Data Coherency
• DataSets support disconnect operation. When
processing is complete, changes are sent back to the
database.
• In a multi-user environment, that obviously can cause
problems.
• Strategies to avoid coherency problems:
– Lock records, so others can read but not update.
– Build the update procedure so that it fails if the affected records
where last changed after you read the data. Then go and
negotiate.
– Allow only one person to update any given area of the data
model, partitioned in some reasonable way for the business.
References
• Programming Microsoft .Net, Jeff Prosise,
Microsoft Press, 2002
• Access Database Design & Programming, Steven
Roman, O’Reilly, 2002
• Professional C#, Robinson et. al., Wrox Press,
2002
• www.w3schools.com/sql/default.asp