Lesson 2 Working with data in a connected environment

 How to use DataReader with data providers? How to retrieving data using a DataReader?. Connection DataReader Database Command Windows Windows Form Form Connected environment...  A ty

Chapter 2

Access data in a

connected environment (cont.)- Lesson 2: Working with data tiếp theo

in a connected environment

 How to use DataReader with data providers?

 How to retrieving data using a DataReader?

What is DataReader?

Connection DataReader Database Command Windows Windows Form Form

Connected environment

 A type that is good for reading data in the most

efficient manner possible

 Read-only, forward-only cursor

 Load only a single row into memory at a time

 Only one DataReader use at a time

 Tie to connection => cannot used other DataReader

 Explicitly close DataReader after used

 DataReader cannot be used for data binding

 Using with stored procedure with a return or output

parameter, must close DataReader before get

parameter value

Features of DataReader

 You can’t access anything until calling Read() the first time

How DataReader works?

 .Read()

 reads a record, and set pointer to the next record

 returns true if there are more rows left to be read

 dataReader[int i]

 dataReader[string colName]

 GetValue(int i)

 returns an object , a value at the i th column or at the

column colName in the current row

 To access column values in native data types:

GetDateTime, GetDouble, GetInt32, GetString,

GetBoolean

Properties and methods of

DataReader

Properties and methods of

 Closes the DataReader

 This allows you to use the Connection for another task

 Using DataReader to retrieve data from Command

private void ToLabel( DataReader dr ) {

private void ToListBox( DataReader dr, ListBox list) {

private void ToListView( DataReader dr, ListView lvw ) {

 A null value in a relational database is used when the value

in a column is unknown or missing

 If you try to retrieve a null value through a DataReader and

assign it to a value type, it causes an InvalidCastException

 The NET framework includes the DBNull class for checking

null value, to distinguish between a null reference and a

null database value

 If the column value is equal to DBNull.Value, it represents a

null database field

 If you want to add a null value to a table in database, use

DBNull.Value

How to check null value

Query with “like”

 Example: get all students with ten is "tuan":

 "select * from sinhvien where ten like '%tuan%' "

 Gets all students with ten is input from TextBox

like '%" + txtTen.Text + "%' "

Note: Query with “like”

Lesson 2: Summary

 Create access database

 Table: Student(ID, FirstName, LastName, Phone)

 Put data in ListView

 Display data to TextBoxes

 Insert new record (using parameter query)

Example 1

 LOP(MaLop, TenLop)

 SINHVIEN(MaSV, Ten, DiaChi, SDT, Lop)

Example 2

 LOP(MaLop, TenLop)

 SINHVIEN(MaSV, Ten, DiaChi, SDT, Lop)

Example 3

 LOP(MaLop, TenLop)

 SINHVIEN(MaSV, Ten, DiaChi, SDT, Lop)

Example 4