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Introduction to ADO.NET
Introduction
This is a set of questions and answers related to
ADO.NET. All the code is in Beta 2. The questions by no means
cover the entire capabilities of ADO.NET. Specifically, I have tried to answer
following questions :
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What is ADO.NET?
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Is ADO.NET different than ADO?
-
What are managed providers?
-
What are the data access namespaces in .NET?
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What are main objects in ADO.NET ?
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How do I establish connection with a database?
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How do I use Command object to execute action queries?
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How do I use command object to execute Select queries?
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How do I use command object to execute stored procedure?
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What is DataAdapter and Dataset?
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How do i populate a dataset?
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How do I navigate dataset?
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How do I add new record?
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How do I change data ?
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How do I delete a row?
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How do I filter data once arrived in data set?
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How do I handle errors ?
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How do I handle transactions?
What is ADO.NET?
ADO.NET is next generation of data access technology from Microsoft target at
.NET platform. ADO.NET is built with
distributed and internet applications in mind. ADO.NET provides strong support for XML and
disconnected data processing.
Is ADO.NET different than ADO?
ADO.NET is much different than ADO. In order to achieve
disconnected data access programmers have to use different techniques
like disconnected recordsets, RDS etc. ADO object model is very small
as compared to ADO.NET. ADO.NET provides number of specialized objects to handle very specific tasks. Microsoft has taken care to
closely map properties and methods of ADO.NET objects with existing ADO counterparts. As per
Microsoft ADO.NET is not a replacement for ADO but an enhancement in the overall data access
technology. You can use both ADO and ADO.NET in your application.
What are managed providers?
A managed provider is analogous to
ODBC driver or OLEDB provider. It performs operation
of communicating with the database. ADO.NET currently provides two distinct managed providers. The SQL Server managed provider is used
with SQL server and is a very efficient way of communicating with SQL Server. OLEDB managed
provider is used to communicate with any OLEDB compliant database like Access or Oracle. The data
access APIs for both the providers are found in separate namespaces.
What are the data access namespaces in .NET?
Following are the most common data access namespaces :
- System.Data
- System.Data.OleDb
- System.Data.SQLClient
- System.Data.SQLTypes
- System.Data.XML
What are main objects in ADO.NET?
Following are the main objects in ADO.NET :
- OleDbConnection / SQLConnection
- OleDbCommand / SQLCommand
- OleDbDataReader / SQLDataReader
- OleDbDataAdapter / SQLDataAdapter
- OleDbParameter / SQLParameter
- DataSet
- DataTable
- DataView
- DataRow
- DataColumn
Most of the objects mentioned above can be created as
'stand-alone' objects via code. In the discussion below we will see all the
examples with OLEDB objects. The usage for SQL server objects is same except
name changes. Also, for simplicity I have omitted the repetitive code
(like opening a database connection) in later examples.
How do I establish connection with a database?
The way you connect to a database is very similar to that used in ADO. You use
connection object to accomplish this. Consider following code fragment :
Dim cnn as OleDbConnection
cnn=new OleDbConnection("OLEDB_connection_string")
cnn.open()
'use connection here
cnn.close()
How do I use Command object to execute action queries?
Using command object is similar to that from ADO.
Dim cmd as OleDbCommand
Dim cnn as
OleDbConnection
cnn=new OleDbConnection("OLEDB_connection_string")
cnn.open()
cmd=
newOleDbCommand("my_action_query",cnn)
cmd.ExecuteNonQuery()
cmd.CommandText=
"new_query"
How do I use command object to execute Select queries?
You can collect records returned by a command object using DataReader object.
Dim dr as OleDbDataReader
Dim cmd as OleDbCommand
Dim cnn as OleDbConnection
cnn=new OleDbConnection("OLEDB_connection_string")
cnn.open()
cmd=new OleDbCommand("my_select_query",cnn)
dr=cmd.ExecuteReader()
do while dr.read()
response.write(dr("field1"))
loop
dr.close()
How do I use command object to execute stored procedure?
You can execute a stored procedure in the same way as any query. Following example
shows how to execute parameterize stored procedure.
Dim cmd as OleDbCommand
Dim p as OleDbParameter
Dim cmd as OleDbCommand
Dim cnn as OleDbConnection
cnn=new OleDbConnection("OLEDB_connection_string")
cnn.open()
cmd=new OleDbCommand("my_stproc_name",cnn)
p=new OleDbParameter("name",type,width)
p.value="myvalue"
cmd.parameters.Add(p)
'add all the parameters in the same way
cmd.ExecuteNonQuery()
What is DataAdapter and Dataset?
Dataset is an in-memory disconnected representation of data
from actual database. Dataset can be thought of as a collection of recordsets. Each
such recordset is called as a DataTable. Note that data table can be
based on JOIN queries. Dataset is much more powerful than a simple
collection of DataTables. You can also put relations and constraints
within various datatables of a dataset. DataSet and its constituent parts like DataTable, DataRow can also be created programmatically.
Since dataset is totally disconnected from the database
there must be some means of communication between the dataset and the database.
DataAdapter is used for that purpose. The main functions performed by DataAdapter are :
Changes made to the dataset are not written to the database unless explicitly updated via DataAdapter.
How do i populate a dataset?
To populate a dataset you will use DataAdapter's Fill
method. One DataAdapter can be used to populate several tables of one or many datasets.
Dim dscmd as OleDbDataAdapter
Dim ds as Dataset
dscmd=new OleDbDataAdapter("sql_select_statement",cnn)
ds=new DataSet()
dscmd.Fill(ds,"data_table_name")
How do I navigate a dataset?
Dim row as DataRow
For each row in ds.Tables("data_table_name").Rows
row.Columns("field1").toString()
Next
How do I add new record to a dataTable?
Dim row as DataRow
row=ds.Tables("recordset_name_in_ds").NewRow()
row("field1")="value1"
row("field1")="value1"
.
.
ds.Tables("recordset_name_in_ds").Rows.Add(row)
dscmd.Update(ds,"data_table_name")
Here, note that you are issuing update on data adapter rather than dataset itself
because dataset is actually a disconnected view of data and you must have valid connection
information to update changes to original database.
How do I change data from a DataTable?
Dim row as DataRow
'i can be any number in below statement
row= ds.Tables("data_table_name").Rows(i)
row("field1")="value1"
row("field1")="value1"
dscmd.update(ds,"data_table_name")
How do I delete a row from a DataTable?
ds.Tables("data_table_name").Rows(i).Delete
dscmd.update(ds,"data_table_name")
How do I filter data once arrived in dataTable?
You can filter data based on some conditions using datatables object's Select
method.
Dim rows() as DataRow
rows=ds.Tables(0).Select("condition_similar_to_where_clause")
How do I handle errors ?
There can be various ways in which you can handle errors. Using try..catch
is most common. ADO.NET also provides a mechanism by which you can set row level error
messages.
Dim cnn as OleDbConnection
Dim cmd as OleDbDataAdapter
Dim ds as Dataset
Dim errors as DataRow()
cnn=new OleDbConnection("connection_string")
cnn.open()
ds=new dataset()
cmd= new
OleDbDataAdapter("select_query",cnn)
cmd.Fill(ds,"data_table_name")
ds.Tables("data_table_name").Rows(0).RowError =
"Some error msg"
ds.Tables("data_table_name").Rows(1).RowError = "Some
other error msg"
if ds.tables("users").HasErrors then
errors = ds.tables("data_table_name").GetErrors()
' do something with erroraneous rows
end if
In above code you can set row level error messages depending on certain business validation. This
will allow us to use common error handling routines. Also, note that the RowError property
is also set by ADO.NET if there is any real database error.
How do I handle transactions?
ADO.NET offers OleDbTransaction object to control a transaction. This object is returned by BeginTransaction
method of OleDbConnection.
Dim tran as OleDbTransaction
Dim cnn as OleDbConnection
cnn=new OleDbConnection("connection_string")
try
cnn.open()
tran=
cnn.BeginTransaction()
cmd=new OleDbCommand("some_sql",cnn)
cmd.Transaction=
tran
cmd.ExecuteNonQuery()
cmd.commandtext=
"some_other_sql"
cmd.ExecuteNonQuery()
tran.Commit()
catch myException as Exception
tran.Rollback()
end try
