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

ADO Application Structure – ASP.Net 1.1

ADO Objects – ASP.Net 1.1

ADO Application Structure – ASP.Net 2.0

ADO Objects - ASP.Net 2.0

Connection Object Methods Properties 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 Connection connection string defining Server and database CommandText Text of SQL query CommandType StoredProcedure | TableDirect | Text (SQL Query) Parameters Arguments for stored procedures Transaction Transaction in which command will execute

DataReader Object Supports one-way, forward-only, access to data. 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. Methods Read() Returns one row and advances current row pointer GetXXX() 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 this[string] Specifies column in row by name, returns value this[int] Specifies column in row by index, returns value FieldCount Number of columns in current row Item Value of a column RecordsAffected Number of rows changed, inserted, or deleted 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: Methods Properties 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 SelectCommand SQL Select text UpdateCommand SQL Update command text InsertCommand SQL Insert command text DeleteCommand SQL Delete command text TableMappings 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 AcceptChanges Commits pending changes to DataSet Clear() Empties all Tables ReadXML(XmlReader) Reads XML data into DataSet WriteXML(XmlWriter) Writes DataSet data to XML file HasChanges() boolean returns true if pending changes AbandonChanges() 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 DataSets hold DataTable members in Table Collection. Properties Rows Rows collection Columns Columns collection TableName Name used in code DataSet Tables Collection Methods Tables.Add(TableName) Tables.Add(DataTable) Tables.AddRange(TableArray) DataTable Rows Collection Properties and Methods Item Value of a specified column Add(DataRow) method to add a new row DataTable Columns Collection Properties ColumnName DataType

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