ASP.NET- accessing the database- datareader vs dataset

- datagrid vs datalist- brief look at web matrix

Accessing the database

1. Open a connection to a database2. Create a recordset to store retrieved data3. Send SQL query to database4. Store answer to SQL query in recordset5. Close connection to database6. Retrieve data from recordset fields to

display onscreen7. Close recordset

Open connection to database (1)

• Work out which connection driver you need

Dim strConn as String

strConn = “Provider=Microsoft.Jet.OLEDB.4.0;Data Source = “ & Server.MapPath(“recruitment.mdb”)

Open connection to database (2)

• Give the string containing driver name & database location to the OleDbConnection

Dim objConn as OleDbConnectionobjConn = New OleDbConnection(strConn)objConn.Open

• You could do both these steps on one line

Create a recordset to store retrieved data

Dim objRS as OleDbDataReader

• Store SQL query in a String

Dim querysql as String

querysql = “SELECT * FROM JobList”

Send SQL query to database &store answer in recordset

Dim strQuery as OleDbCommandstrQuery = New OleDbCommand(querysql,

objConn)

objRS = strQuery.ExecuteReader

• Close connection to databaseobjConn.Close

Retrieve data from recordset to display onscreen

JobDataGrid.DataSource()=objRSJobDataGrid.DataBind()

• Close recordset

strQuery.DisposeobjRS.Close

DataReader vs DataSet

DataReader vs DataSet

• Extremely simplified summary:• DataReader

– Conveyer belt of data from database to .NET application (bridge)

• DataSet– Miniature in-memory copy of the database

(usually just part of it)

DataReader

• Remains connected to the database– Only contains one row at a time– Can only go forwards– Can’t edit the data directly

• Different types for each provider– Microsoft uses OleDbConnection– SQL uses SQLConnection

• 30 (ish) times faster than a dataset • Can be looped so all data is retrieved and stored in a

table in memory

DataSet

• Disconnected– Retrieves all info in one go & stores in memory

• Editable• Provider neutral

– can also be used to access XML files

• Can be sorted or searched• Very good for basic data-entry applications• Useful for caching information to be shown on

several pages across your website

DataGrid vs DataList

• Extremely simplified summary:• DataGrid

– table

• DataList– List– You design the layout yourself

DataGrid

• Most versatile, but least flexible• Built-in paging, sorting & editing facilities• Each row displays 1 record• Can be nested• Slowest to display on screen

DataGrid column types• Bound Column

– Value from datasource as plain text

• Button Column• Edit Column• HyperLink Column

– Hyperlink, text & url may come from datasource

• Template Column– Customise html output of the column (allows

nested grids)

DataList

• No built-in support for paging, sorting & editing

• Can display more than 1 record on each row• Much more customisation of data layout is

possible• Can be nested (not as easy as datagrid)

DataList templates

• Header template• Item template

– Displayed once per row from recordset– Can be set to repeat using <table> or <span> HTML tags

• Alternating Item Template• Edit Item Template• Selected Item Template• Separator Template• Footer Template

Initial View

Data Tab – click here to establish connection to database

DataGrid

HTML tab- Shows HTML code only

Code tab- Shows ASP.NET code only

All code at once

Drag & drop

Drag & dropbasic query buildersThis menu only visible in code tab

Auto-generated SELECT function

Links datagrid to function when page is loaded

TO DO

• Oasisplus– ASP.NET : Activities 1 & 2