Chapter 4. Windows Database Using Related Tables The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill

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1 Chapter 4 Windows Database Using Related Tables McGraw-Hill 2010 The McGraw-Hill Companies, Inc. All rights reserved.

2 Objectives - 1 Explain the types of table relationships Display master/detail records Display a field from a second table using a lookup Create a search using a parameterized query and write a filter to retrieve specific data Assign data values to unbound controls McGraw-Hill 4-2

3 Objectives - 2 Retrieve and display the parent row for a selected child row Retrieve and display an array of child rows for a selected parent row Create an application that displays from a many-to-many relationship Select the correct locations for handling and formatting data in a multitier application McGraw-Hill 4-3

4 Data Relationships - 1 Data stored in multiple related tables Primary table is the parent or master Second table is the child or detail Table relationships may be One-to-one (1:1) One-to-many (1:M) Many-to-many (M:N) McGraw-Hill 4-4

5 Data Relationships - 2 Each table usually has a field or fields called the primary key Uniquely identifies each record The primary key of one table is included as a field in a related table to link the two tables That field is called a foreign key The foreign key is common to both tables McGraw-Hill 4-5

6 One-to-Many Relationships Most common type of relationship One record in the parent table relates to one or more records in the child table Examples include: Customer with multiple orders Department with multiple employees Student with multiple courses A row in the parent table can have many matching rows in the child table A row in the child table has only one matching row in the parent McGraw-Hill 4-6

7 Many-to-Many Relationships Example: One author can write many books; one book can have many authors SQL Server and Access require a junction table to join two tables The junction table s primary key consists of the foreign keys from both tables McGraw-Hill 4-7

8 One-to-One Relationships Least common relationship One record in the parent matches one record in the child table Usually the two tables can be combined but may be kept separate for several reasons Security, the child table contains short-term information, or updates are more efficient with the separation McGraw-Hill 4-8

9 Constraints Relationships may require the use of constraints A unique constraint specifies that no duplicate entries are allowed in a column Foreign-key constraints ensure that parent and child tables remain synchronized when records are deleted or changed A concept called referential integrity McGraw-Hill 4-9

10 The DataSet object in ADO.NET can hold more than one table and the relationships between the tables To generate a DataSet with multiple tables, check the boxes for all desired tables in the Data Source Configuration Wizard Creating a Dataset with More Than One Table McGraw-Hill 4-10

11 Viewing or Setting a Relationship A DataRelation object describes the relationship between the tables Open the.xsd file for the DataSet to view or create the relationship The parent is always the one side of the one-tomany relationship McGraw-Hill 4-11

12 Specifying the Parent, Child, and Foreign Key When a relationship is added to a DataSet s schema, the parent/child relationship must be right Determine which table is the one side and which is the many side in a one-tomany relationship The one side should always be the parent and the many side should be the child McGraw-Hill 4-12

13 Queries and Filters A parameterized query creates a new DataSet A filter selects records from an existing DataSet Choose a filter or parameterized query depending on the needs of the application McGraw-Hill 4-13

14 Using a Parameterized Query SQL statement that retrieves selected record(s) based on a value that the user enters at run time The value supplied by the user is called the parameter, which is the basis for the term parameterized query A TableAdapter property holds queries for selecting a DataSet s data McGraw-Hill 4-14

15 Selecting Specific Records Modify the SQL SELECT statement used by the TableAdapter to have a DataSet contain only selected records Use a WHERE clause in a SQL query to specify which records to select, called the criteria When the value for the WHERE clause is not known until run time, use a wildcard in place of the actual value Supply the value as a parameter in code McGraw-Hill 4-15

16 Creating a Parameterized Query Enter the parameter in the Filter column and the WHERE clause is created The grid fills with the selected records McGraw-Hill 4-16

17 Filtering a DataSet Select rows from an existing DataSet using a filter Use the BindingSource s Filter method McGraw-Hill 4-17

18 Writing a Filter Rules for creating a filter are the same as for a WHERE clause of an SQL statement Specify the field, a comparison operator (usually the equal sign), and the value to match LastName = Jones SalesAmount = 1000 Quantity > 0 Use single quotes to enclose the value to match when a string contains spaces Title = A Great Book McGraw-Hill 4-18

19 Comparison Operators McGraw-Hill 4-19

20 Binding a List at Run Time List usually appears empty until a selection is made Bind the control in code rather than at design time When the DataSource is set, the list fills with the data from the BindingSource ' Bind the list box with the filtered data. With EmployeeListBox.DataSource = BindingSource1.DisplayMember = "Name" End With McGraw-Hill 4-20

21 Filtering a DataSet User selects a job description from the combo box The corresponding job_id is used to filter the data All matching records display in the list box McGraw-Hill 4-21

22 Unbound Data Fields DataRelation object Relate parent and child records Retrieve a selected parent row Retrieve an array of matching child rows Refer to individual fields in selected rows Assign data values to a property of an unbound control Controls that do not have any data bindings established Refer to the relations between tables by name Give each relation a meaningful name McGraw-Hill 4-22

23 Referring to Records and Fields - 1 Actual data values are held in DataRow objects Each Table object in a DataSet has a DataRows collection made up of DataRow objects The data values are held in the DataRow.Items collection McGraw-Hill 4-23

24 Referring to Records and Fields - 2 Use any of the following statements to retrieve a field from a DataRow object FirstNameString = EmployeeDataRow.Item(1).ToString or FirstNameString = EmployeeDataRow.Item( fname ).ToString or FirstNameString = EmployeeDataRow!fname.ToString McGraw-Hill 4-24

25 Retrieving a Related Parent Row Allow a user to select a value from a bound combo box Write code to retrieve data in the SelectionChangeCommitted event handler Find the row in the table that matches the combo box selection Use the GetParentRow method to retrieve the matching row from the table Retrieve the specific data item and assign it to the Text property of a text box McGraw-Hill 4-25

26 Retrieving Related Child Rows Similar to retrieving a related parent row GetChildRows method returns an array of rows rather than a single row McGraw-Hill 4-26

27 Many-to-Many Relationships Requires a third table, a junction table In relationships, the junction table is the child table in the relationships with each of the parent tables McGraw-Hill 4-27

28 Multitier Considerations Think through the goals of OOP when separating an application into multiple classes Presentation tier should provide only the user interface User input and output formatting belongs in the form Data retrieval and processing should be handled in other classes McGraw-Hill 4-28

29 Formatting a Grid at Run Time Format the columns of a DataGridView at run time Binding the grid resets all properties If the program performs binding, place the statements to format the columns after binding is complete McGraw-Hill 4-29