Download Active Data Objects in .Net

Active Data Objects
Binding ASP.NET Controls to Data
Jim Fawcett
CSE686 – Internet Programming
Summer 2005
Support for Data in .Net
• Connected data access:
– Use Connection object and Command to connect a DataReader
object to database and read iteratively.
– There are two flavors of these objects, Sql--- and OleDb---. The
first are tuned to SQL Server and the second can connect to any
database the provides drivers, e.g., Access, SQL, Oracle, …
• Disconnected data access:
– Use a SqlDataSource and GridView or DetailsView or DataList or
FormView or Repeater and execute an SQL query or stored
procedure.
– 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 Application Structure – ASP.Net 1.1
Data Providers
Data Consumers
Disconnected Access to Tables
SqlDataAdapter
DataSet
WinForm
Single Item or flag
SqlConnection
SqlCommand
WebForm
Connected cursor reads rows
SqlDataReader
database
ADO Objects – ASP.Net 1.1
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
ADO Application Structure – ASP.Net 2.0
Data Providers
Data Consumers
Disconnected Access to Tables
SqlDataSource
GridView
WebForm
Connection
Property
Command
Properties
DetailsView
DataList
database
ADO Objects - ASP.Net 2.0
SqlDataSource
Command
SelectCommand(Type)
Connection
UpdateCommand(Type)
Connection
CommandText
ConnectionString
InsertCommand(Type)
CommandType
DeleteCommand(Type)
Many More Properties
database
GridView
Rows Collection
Columns Collection
Connection Object
• Methods
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Open()
Close()
BeginTransaction()
BeginTransaction().Commit()
• Properties
– ConnectionString
• Windows, SQL, or Forms Authentication
• For Windows authentication:
– "server=HINDENBURG\\NETSDK;Integrated Security=SSPI; Trusted_Connection=yes;
database=pubs“
– Also need impersonation code in asp application – see link on CSE686 page.
– Database, Datasource, State (open | closed) are readonly properties
• You can drag a connection object onto a form
– Doesn’t identify a data source
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
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–
–
–
–
Connection
CommandText
CommandType
Parameters
Transaction
connection string defining Server and database
Text of SQL query
StoredProcedure | TableDirect | Text (SQL Query)
Arguments for stored procedures
Transaction in which command will execute
DataReader Object
•
Supports one-way, forward-only, access to data.
•
Methods
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–
–
–
–
–
–
Once data has been read, must be closed and re-created to access data again.
DataReader lasts as long as the connection is open. It can’t be persisted to session.
Read()
GetXXX()
Returns one row and advances current row pointer
GetBoolean, GetInt16, GetChars, GetString, GetValue, …
37 different methods for specific XXX types
GetFieldType Returns type of specified column
GetSchemaTable
Returns DataTable describing structure of data
NextResult
Advances current row pointer
Close()
Closes DataReader
•
Properties
•
Normally, a DataReader is returned from a command object, ready to bind to a
display control. You get one from the command method ExecuteReader().
–
–
–
–
–
this[string]
this[int]
FieldCount
Item
RecordsAffected
Specifies column in row by name, returns value
Specifies column in row by index, returns value
Number of columns in current row
Value of a column
Number of rows changed, inserted, or deleted
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)
Loads data from source into DataSet
– FillSchema(DataSet, SchemaType)
– Update()
Returns modified data to source
• Properties
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–
–
–
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SelectCommand
UpdateCommand
InsertCommand
DeleteCommand
TableMappings
SQL Select text
SQL Update command text
SQL Insert command text
SQL Delete command text
Map for source and DataSet columns
DataSet Object
• Used for Disconnected manipulation of a source’s data.
– Read-write, can access tables in any order, as often as you like.
– Lasts only as long as the page that created it, unless persisted to
session or some other mechanism.
• Methods
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–
–
–
–
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AcceptChanges
Clear()
ReadXML(XmlReader)
WriteXML(XmlWriter)
HasChanges()
AbandonChanges()
Commits pending changes to DataSet
Empties all Tables
Reads XML data into DataSet
Writes DataSet data to XML file
boolean returns true if pending changes
Reverts to unchanged state
• Properties
– Tables collection
• ds.Tables[tableStr].Rows[3]["Responsible Individual"] = userID;
– Relations collection
Relationships between Tables in DataSet
• Normally, you don’t fill the DataSet, a DataAdapter does that.
DataTable Object
•
Holds records from a source per TableMapping
•
Properties
– DataSets hold DataTable members in Table Collection.
– Rows
Rows collection
– Columns
Columns collection
– TableName Name used in code
•
DataSet Tables Collection Methods
•
DataTable Rows Collection Properties and Methods
•
DataTable Columns Collection Properties
– Tables.Add(TableName)
– Tables.Add(DataTable)
– Tables.AddRange(TableArray)
– Item
– Add(DataRow)
– ColumnName
– DataType
Value of a specified column
method to add a new row
SqlDataSource
• Used to connect Connection Object to GridView or
DetailsView or DropDownList or … objects and execute
commands.
• Methods
– DataBind()
• Calls Select(), called by view controls DataBind() method.
– Delete(), Insert(), Select(), Update()
• Executes command defined DeleteCommand, InsertCommand,
SelectCommand, or UpdateCommand
• Properties
– ConnectionString connection string defining Server and database
– Commands
DeleteCommand, InsertCommand,
SelectCommand, UpdateCommand
– CommandTypes DeleteCommandType, …
StoredProcedure | Text (SQL Query)
– Parameters
DeleteParameters, …
Arguments for stored procedures
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.
• ADO.Net does not directly provide locks
• You can:
SqlTransaction t = conn.BeginTransaction(IsolationLevel.Serializable);
some code here
t.Commit();
• Do this in a try, catch block with finalizer that does the commit so you don’t
leave a bunch of records locked indefinately if your code throws an exception.
– 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
• Pro ASP.NET 2.0 in C# 2005, MacDonald &
Szpuszta, Apress, 2006
• Programming Microsoft .Net, Jeff Prosise,
Microsoft Press, 2002
• Professional C#, Robinson et. al., Wrox Press,
2002
• www.w3schools.com/sql/default.asp