How to: Design a Query by Using the Query Designer
A query returns data that meets certain criteria. For more information, see Queries: Retrieving Information from a Data Source. Use a query to display information in a screen. You can also use the results of a query in your custom business logic.
To begin, add a query to the project. For more information, see How to: Add, Remove, and Modify a Query. The query automatically opens in the query designer. In the query designer, design a query by performing any of the following tasks:
Add Filter Conditions.
A filter condition describes a test that each row of data must pass to be included in the results.
Use a Parameter in a Filter Condition.
Users of the application can provide a parameter value at run time by typing information or making selections on the user interface (UI).
Group Filter Conditions Together.
Use filter groups to ensure that a set of filter conditions are evaluated together as a single unit separate from the rest of the filter conditions.
Add Sort Terms.
Sort terms enable you to set the initial sort order of the data rows that are returned by a query.
Reorder Filter Conditions, Filter Groups, Sort Terms, and Parameters.
You can change the order in which filter conditions, filter groups, sort terms, and parameters are evaluated in the query.
Add Filter Conditions
Filter conditions specify the data rows that you want the query to return. For example, you can add a filter condition that returns only customers who are located in New York. A filter condition is the same as a search condition in the WHERE clause of a traditional SQL statement. Filter conditions contain a selection property, an operator, a comparison type, and a comparison value. Filter conditions are separated by Boolean operators.
The following illustration shows the parts of a filter condition.
.png "Filter conditions in a query")
To add a filter condition
In the Query Designer, expand the Filter section of the query.
In the Filter section, click Add Filter.
A filter condition is added to the Filter section. Several drop-down lists and a text box appear next to the filter condition.
In the first drop-down list, select one of the following conditions:
Select Where to return all data rows that comply with the rest of the filter condition.
Select Where Not to return data rows that do not comply with the rest of the filter condition.
In the second drop-down list, select the property that you want to use for the filter condition.
For example, if you want the query to return sales orders that have a specific order date, the selection property is OrderDate.
In the third drop-down list, select the operator that you want to use.
For example, to return sales orders that have an order date that is before 9/22/2009 12:00:00 AM, select the < (less than) operator.
Add a comparison value. To accomplish this, click the button next to the text box that appears at the end of the filter condition, and then click one of the following buttons:
Click Literal to type the value that you want to use as the comparison value.
Click Property to use a property as the comparison value.
If you select this option, the text box becomes a drop-down list.
Click Parameter to add a parameter as a comparison value.
If you select this option, the text box becomes a drop-down list.
Note
For certain types of fields, such as DateTime fields, you can click Global to use relative values such as Now, Today, or Start of Week.
In the drop-down list or text box that appears at the end of the filter condition, perform one of the following steps:
If you select Literal in the previous step, type a value such as 9/22/2009 12:00:00 AM.
If you select Property in the previous step, select or type the name of the property.
If you select Parameter in the previous step, select a parameter.
Repeat steps 2-7 to add as many filter conditions to the query as you want.
You can relate a filter condition to other filter conditions by using one of the following Boolean operators: And, Or, And Not, Or Not.
Use a Parameter in a Filter Condition
You can add a parameter as a comparison value in a filter condition. You can design screens that enable users to provide this value at run time. You can also provide this value as a parameter to the query method if you execute the query from your custom business logic.
To add a parameter to a query
In the Query Designer, expand the Parameter section.
In the Parameter section of the designer, click Add Parameter.
A parameter is added to the Parameter section. A text box and a drop-down list appear as part of the parameter.
In the text box of the parameter, provide a name (for example, SalesTerritory).
In the drop-down list of the parameter, select the data type of the parameter (for example, String).
On the View menu, click Properties Window.
In the Properties window, click or clear the Is Optional checkbox.
Select the Is Optional checkbox, if you want the query to exclude filter conditions that use the parameter when the value of the parameter is null.
Clear the Is Optional checkbox, if you want the query to always include filter conditions that use the parameter even when the value of the parameter is null. If the value of the parameter is null, the null value will be used as the comparison value when evaluating the filter condition..
In the Query Designer, expand the Filter section.
In the Filter section of the designer, point to the filter condition, click the button at the end of the filter condition, and then click Parameter.
In the drop-down list next to the button, select the parameter.
You can enable users to type or select parameter values in a screen. For example, you can design a screen that enables a user to view a list of customers by selecting a sales territory.
Alternatively, you can bind the parameter to properties from other lists. For example, you could design a screen that enables a user to view a list of sales orders by selecting a customer. For information about how to enable users to provide a parameter value on a screen, see How to: Provide a Value to a Query Parameter.
Group Filter Conditions Together
You can group filter conditions together so that they are evaluated as a unit. Grouping filter conditions is like putting parentheses around expressions in an SQL statement. Expressions in parentheses are evaluated before other expressions in the statement.
The following illustration shows two filter groups.
.png "Filter groups in a query")
To create a filter group
In the Query Designer, expand the Filter section.
In the Filter section of the designer, point to Add Filter, click the down arrow, and then click Group.
A filter group is added to the Filter section. A new filter condition is added to the filter group.
To add filter conditions to a filter group
Perform one of the following steps:
At the bottom of the filter group, click Add Filter.
Note
The Add Filter button appears at the end of the line that delineates the filter group.
From the Filter section of the designer, drag any existing filter condition to the filter group.
To add a filter group to another filter group
Perform one of the following steps:
At the bottom of the filter group, point to Add Filter, click the down arrow, and then click Group.
Note
The Add Filter button appears at the end of the line that delineates the filter group.
From the Filter section of the designer, drag any existing filter group to the filter group.
The child filter group is enclosed in the parent filter group.
You can relate a filter groups to other conditions and groups in the query by using one of the following Boolean operators: And, Or, And Not, Or Not.
Add Sort Terms
You can specify the order in which the results of a query appear by adding one or more sort terms. A sort term is similar to a column in the ORDER BY clause of a traditional SQL statement.
To sort the results of a query
In the Query Designer, expand the Sort section.
In the Sort section of the designer, click Add Sort.
A sort term is added to the list of sort terms. Two drop-down lists appear next to the sort term.
In the first drop-down list, select the property that you want to use for the sort term. For example, to sort contacts by their last name, select the LastName property of the Contact entity.
In the second drop-down list, select one of the following items:
Select Ascending to sort results from least to greatest. For example, last names that start with the letter A appear first. Last names that start with the letter Z appear last.
Select Descending to sort results in order from greatest to least. For example, last names that start with the letter Z appear first. Last names that start with the letter A appear last.
Repeat steps 2-4 to add as many sort terms to the query as you want.
Sort terms only set the initial sort order of data rows that appear in a screen. Users can view data rows in a different order by interacting with the screen.
Reorder Filter Conditions, Filter Groups, Sort Terms, and Parameters
You can change the order in which filter conditions, filter groups, sort terms, and parameters are evaluated in the query.
To reorder Filter Conditions and Filter Groups
In the Query Designer, expand the Filter section.
In the Filter section of the designer, drag a filter condition or filter group to a location that is higher or lower in the list.
To reorder Sort Terms
In the Query Designer, expand the Sort section.
In the Sort section of the designer, drag a sort term to a location that is higher or lower in the list.
Changing the order of sort terms affects how the data is sorted in the query results. For example, assume two sort terms, one that sorts the data by SalesTerritory, and another that sorts by OrderDate. In this example, orders would be sorted by SalesTerritory first. Then, orders within each SalesTerritory group would be sorted by their order dates.
To reorder Parameters
In the Query Designer, expand the Parameters section.
In the Parameters section of the designer, drag a parameter to a location that is higher or lower in the list.
Next Steps
To learn how to use a query in a screen, see How to: Create a Silverlight Screen.
To learn how to extend a query in ways that go beyond the capabilities of the query designer, see How to: Extend a Query by Using Code.
See Also
Tasks
How to: Provide a Value to a Query Parameter
How to: Extend a Query by Using Code
How to: Retrieve Data from a Query by Using Code
How to: Add, Remove, and Modify a Query
Walkthrough: Designing a Screen