Navigating database with windows forms.

Tiered applications  Provide a means to develop many presentations of the same app  Makes changes to the back end easier when it is not tied into the front end (presentation Tier)

 Provides more portability for code created in each business app.  Provides a way to create a Data connection that is a web service on a network.  Can easily create multiple apps for different platforms at the same time.  Apps for mobile devices  Apps for Windows  Apps for the web

 You have three basic tiers  Presentation (The form or front end)  Business  Used to make all the calculated values in the form  Enforces the Business rules of your application  Enforces data validation  Data Tier (Provides connections and manages rules (SQL) of the database)  The data tier can be created for any DBMS  Can be a Windows/Web service providing data to multiple apps on a network.

 To create a Data Tier  Right click on the project and select new Item  Select new class  This class will contain references to the TableAdapters and DataSet  The TableAdapter contains the Connection, DataAdapters and Command Objects that are needed for the data Tier.  To access these objects and all methods and properties, require the use of Accessor methods/sub procedures that you must create

 Two methods are needed in the data tier 1. A function that will return a reference to the datset to the form (getDataSet()). 2. A sub procedure that will provide access to the Update method of the TableAdapter (setDB()) AS a refresher  All SQL statements are managed by the DataAdapter located inside the TableAdapter.  All Connections to the database are managed by the connection object which is also located inside the TableAdapter.  A local copy of the database in the DataSet

 DataSets hold a local copy of the database.  Any changes of the dataset have to be pushed back to the server  The Update Function in the TableAdapter takes only the rows of data that have changed and then push them onto the database.  The Accept method of the DataSet is needs to be called once an update is performed.  The Accept method clears all flags associated with rows that have been updated.

 Data can change on a DBMS on a network frequently  Once an update occurs, the DataSet must accept all changes that Occur in the DBMS  The AcceptChanges() function of the datset must be called after an update is made

Form design and changing data in a database

 When adding or editing a record in the data set  all navigation should be disabled.  This prevents the user from accidentally moving the position of the record during an edit.  All other buttons should be disabled  i.e. Edit and Delete buttons  Separate sub procedures should be created to do this  EnableNav()  EnableEdit()

 When a form opens  All textboxes should be disabled and ready for navigation  Buttons that are not needed should also be disabled (i.e. Cancel button)  With the enable navigation function you have a choice of disabling the control or to make it Read only (programmer preverence)  The enable Edit will  Enable all the textboxes and disable all navigation.  By disabling navigation during edits, you prevent accidently editing a different record in the DB  The edit or Add button’s text should change to a save button. This saves on Form real estate.

Private Sub enableNav() txtFirstNAme.Enabled = False txtLastName.Enabled = False txtAddress.Enabled = False txtCity.Enabled = False txtState.Enabled = False txtZip.Enabled = False btnNext.Enabled = True btnPrev.Enabled = True btnCancel.Enabled = False End Sub

Private Sub disableNav() txtFirstNAme.Enabled = True txtLastName.Enabled = True txtAddress.Enabled = True txtCity.Enabled = True txtState.Enabled = True txtZip.Enabled = True btnPrev.Enabled = False btnNext.Enabled = False btnCancel.Enabled = True End Sub

 The Binding Manager object in the form contains an AddNew() Sub Procedure which  clears all bound textboxes  Moves the position of the record to the end  Auto increments all key id fields (if they are set for auto increment)  This sub procedure is needed in the event handler of the Add Button in order for users to add a record to the DB.

 Buttons can also be used for two purposes  With the Add button  Click once it places the form in a position to add a record  Once the information is added to the text fields, the button can be clicked again to save the record (code provided to student).

 There are specific steps that are taken to save a record to a database 1. Call the EndEdit() sub procedure in the Binding Manager object 2. Call the setDB() sub procedure in the DataTier This sub procedure in the Data Tier will call the update method in the Table Adapter. (please read tutorial on how to create the data tier) 3. Call the AccpetChanges sub procedure in the DataSet (also located in the data tier) Taken these steps in this order will ensure that all the data will be saved to the database