1. Performing Data Updates
Objectives
In this lesson, you will learn to:
Perform cached data updates
Perform direct data updates
Identify the need for concurrency management
Identify the methods of maintaining concurrency in datasets
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2. Performing Data Updates
Problem Statement 7.D.1
The Diaz Telecommunications Sales Manager needs to view
the customer details in a customized format. In addition, the
customer details need to be maintained, which involves
adding new customer details, and modifying and deleting the
existing ones.
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3. Performing Data Updates
Task List
Identify the data that needs to be maintained.
Identify the mechanism to maintain data.
Design a Windows Form to maintain the data.
Connect to the database.
Bind the data to the Windows Form controls.
Write the code to maintain the data.
Perform data maintenance.
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4. Performing Data Updates
Task 1: Identify the data that needs to be maintained.
Result:
As per the given problem statement, the data to be
maintained is as follows:
CustID
FName
LName
Address
Phone
email
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5. Performing Data Updates
Task 2: Identify the mechanism to maintain data.
Data can be retrieved from a database directly through
data commands or cached in datasets.
Performing cached data updates
Updating the dataset
® While updating the dataset, some events are raised:
® ColumnChanging
® RowChanging
® ColumnChanged
® RowChanged
® RowDeleting
® RowDeleted
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6. Performing Data Updates
Task 2: Identify the mechanism to maintain data.
(Contd.)
® Whileupdating the dataset, the following information
is maintained:
® RowState property
® Unchanged
® Added
® Deleted
® Detached
® Modified
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7. Performing Data Updates
Task 2: Identify the mechanism to maintain data.
(Contd.)
® DataRowVersion Enumeration
® Original
® Current
® Proposed
® Default
® The changes are committed to the dataset by calling
the AcceptChanges()method.
Updating the data source
® Thedata source is updated with the changed
dataset by calling the Update()method of the data
adapter.
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8. Performing Data Updates
Just a Minute…
2. When does the RowState property have the value
Detached?
3. What is the relationship between the RowState property
and the DataRowVersion enumeration?
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9. Performing Data Updates
Task 2: Identify the mechanism to maintain data.
(Contd.)
Performing direct data updates
Data commands are can be used to directly update the
data source.
A data command object can be derived from the
OleDbCommand class or the SqlCommand class.
For executing a data command, the Connection,
CommandText, and the Parameters properties for the
data command have to be set.
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10. Performing Data Updates
Task 2: Identify the mechanism to maintain data.
(Contd.)
Result:
Since you need to access the data through a dataset, you
will perform a cached data update.
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11. Performing Data Updates
Just a Minute…
1. In which cases, direct data update is preferred to updates
through datasets?
2. Write a code to connect to a database through data
commands.
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12. Performing Data Updates
Task 3: Design a Windows Form to maintain the data.
Task 4: Connect to the database.
Task 5: Bind the data to the Windows Form controls.
Task 6: Write the code to maintain the data.
Task 7: Perform data maintenance.
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13. Performing Data Updates
Maintaining Data Concurrency
Concurrency control is the process of ensuring that in case
many people attempt to modify data in a database at
the same time, modifications made by one person do not
adversely affect those of another person.
Method Description
Pessimistic concurrency control In this type of concurrency control, a system of
locks applied does not allow users to modify data
in a way that affects other users. When a lock is
applied, other users cannot perform actions that
would conflict with the lock until the owner
releases it. Pessimistic control is mainly used in
environments where the data contention is high
and protecting data with locks is less costly than
rolling back transactions in case of concurrency
conflicts. Pessimistic concurrency is not possible
in a disconnected architecture.
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14. Performing Data Updates
Maintaining Data Concurrency (Contd.)
Method Description
Optimistic concurrency control In this type of concurrency control, the lock is not
applied when the users read the data. When the
user performs a data update, the system checks to
see if the data has been changed by another user
after the data was read. If the data has been
changed, an error is raised. Optimistic concurrency
is used in environments where the data contention
is low and protecting data with locks is more costly
than rolling back transaction in case of concurrency
conflicts.
‘Last in Wins’ concurrency control This type of concurrency control works in a similar
way as the optimistic concurrency control, with the
difference that the record is updated regardless of
whether the record has been changed or not.
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15. Performing Data Updates
Maintaining Data Concurrency (Contd.)
ADO.NET implements optimistic concurrency by using the
following two methods:
The Version number method
® Theversion number method requires the record to
be updated to have a datetime stamp or a version
number column.
The saving all values method
® When the data is retrieved, a copy of all fields, that
is, the original version is maintained on the client.
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16. Performing Data Updates
Just a Minute…
What is the difference between the concurrency control
through the Saving All method and the Version Number
method?
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17. Performing Data Updates
Optimistic Concurrency through Data Adapter
By default, the data adapters that are created in an
application implement optimistic concurrency.
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18. Performing Data Updates
Problem Statement 7.P.1
The Sales Manager of Diaz Telecommunications needs to
maintain customer details, which involves adding new
customer details, and modifying and deleting existing
customer details. While adding and modifying details, the
application should ensure that no field is left blank.
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19. Performing Data Updates
Summary
In this lesson, you learned that:
Data can be retrieved from a database directly through data
commands or can be cached in datasets.
When a dataset is used to access data, updating the
database consists of two steps, updating the dataset and
updating the database.
When you make changes to a record in the table, the
following events are raised by the DataTable object:
ColumnChanging
RowChanging
ColumnChanged
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20. Performing Data Updates
Summary (Contd.)
RowChanged
RowDeleting
RowDeleted
The ColumnChanging and RowChanging events raised by
the DataTable object are used to validate the dataset
while updating it.
When changes are made in a dataset, that is, a row is
added, deleted, or modified, some information about each
update has to be maintained.
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21. Performing Data Updates
Summary (Contd.)
The data adapter uses the following information while
updating the data source:
The RowState property — The RowState property of the
DataRow object indicates the current state of the
record.
The DataRowVersion enumeration — A dataset can
maintain four versions of a DataRow object: Current,
Original, Proposed, and Default.
After the changes have been made, they are committed to
the dataset by calling the AcceptChanges() method of the
dataset to accept the changes made to the dataset.
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22. Performing Data Updates
Summary (Contd.)
The data source is updated with the changed dataset by
calling the Update() method of the OleDbDataAdapter class.
Data commands are generally used in the following cases:
To work with stored procedures that return a result set,
which can be manipulated
To access data that is not appropriate for storing in a
dataset, such as data with a short life cycle
To access read-only data, that is, data that will not be
updated
A data command object can be derived from the
OleDbCommand class or the SqlCommand class.
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23. Performing Data Updates
Summary (Contd.)
A data command object can be derived from the
OleDbCommand class or the SqlCommand class.
For executing a data command, the Connection and
the CommandText properties for the command
have to be set for specifying the connection and the
SQL query to be executed to retrieve the data,
respectively.
‘Concurrency’ means ‘at the same time’; thus,
concurrency management means to decide the action
that will take place when multiple users try to
update the same record.
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24. Performing Data Updates
Summary (Contd.)
There are three concurrency management methods
available:
Pessimistic concurrency control — In this type of
concurrency control, a record is not available to other
users from the time that a user begins to edit the record
till the time that the record is updated in the database.
Optimistic concurrency control — In this type of
concurrency control, the record is not available to other
users only when the record is being updated in the
database. When a user tries to update a record that has
been changed, an error occurs.
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25. Performing Data Updates
Summary (Contd.)
Last in Wins concurrency control — This type of
concurrency control works similar to the optimistic
concurrency control, the only difference being that the
record is updated without checking whether the record
has been changed or not.
When the row is changed and there is an attempt to
update the database, ADO.NET uses two methods to
determine if any changes have occurred:
The Version number method
The saving all values method
By default, the data adapters that are created in an
application implement optimistic concurrency.
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