Retrieving database data using ObjectQuery API

Kentico uses ObjectQuery to provide an abstraction layer over the SQL database. Developers use ObjectQuery to retrieve data from the Kentico database. The main advantages of using ObjectQuery are:

• strongly typed and enumerable results
• independence on specific versions of SQL syntax
• security

ObjectQuery call example:

var query = UserInfoProvider.GetUsers();

The example query retrieves all users stored within Kentico.

The resulting data set contains Info objects. One instance of an Info object represents one row of data from the database. In this case, the result is a set of UserInfo objects. The result allows you to iterate through the records using a foreach statement.

Similarly to users, you can use ObjectQuery to retrieve any other type of object. To do that, use the correct InfoProvider class and the GetX method, where X is the object name. The following table provides an example of the naming conventions.

Selecting only specific columns

ObjectQuery allows you to select only those columns that you need to work with. Selecting only the required columns is a good practice that prevents issues with performance of your code by transferring only the necessary amount of data from the database server to the application server.

var columnsQuery = UserInfoProvider.GetUsers()
    .Columns("FirstName", "LastName", "UserName");

This example query retrieves all users but limits the data to the users’ first names, last names, and usernames.

Limiting the retrieved results (SQL WHERE)

ObjectQuery provides a way to narrow down the resulting data using SQL syntax independent where conditions.

Use predefined where condition methods that provide optimized performance and make your code easily readable. The predefined where condition methods include, but are not limited to:

• WhereEquals(“ColumnName”, value) - checks the equality of the value in the specified column with the value specified in the second parameter.
• WhereGreaterThan(“ColumnName”, value) - compares the value in the specified column with the second parameter.
• WhereNull(“ColumnName”) - select only rows where the specified column has a NULL value.
• WhereNot(whereCondition) - negates the specified where condition.
• WhereStartsWith(“ColumnName”, “Value”) - only works for text columns. Selects only rows whose value in the specified column starts with the given value.

You can find the full list of predefined where conditions in the Kentico API Reference.

// Retrieves all users whose first name is "Joe"
var whereQuery = UserInfoProvider.GetUsers().WhereEquals("FirstName", "Joe");

Logical operators

ObjectQuery allows you to join together multiple where conditions.

• By default, the conditions are combined using an AND parameter.
• To place an OR operator between conditions, call the Or() method between the given Where methods.
• You can also explicitly call the And() method if you wish to make the code of your conditions clearer and easier to read.

Example 1:

// Retrieves users whose first name is "Joe" or last name is "Smith"
var whereQuery = UserInfoProvider.GetUsers()
    .Where("FirstName", QueryOperator.Equals, "Joe")
    .Or()
    .Where("LastName", QueryOperator.Equals, "Smith");

DECLARE @FirstName nvarchar(max) = N'Joe';
DECLARE @LastName nvarchar(max) = N'Smith';

...

WHERE [FirstName] = @FirstName OR [LastName] = @LastName

Example 2:

// Retrieves all enabled users whose first name is "Joe" and email address ends with "localhost.local"
var whereQuery = UserInfoProvider.GetUsers()
    .WhereEquals("FirstName", "Joe")
    .WhereEquals("UserEnabled", 1)
    .WhereEndsWith("Email", "localhost.local");

DECLARE @FirstName nvarchar(max) = N'John';
DECLARE @UserEnabled int = 1;
DECLARE @Email nvarchar(max) = N'%localhost.local';

...

WHERE [FirstName] = @FirstName AND [UserEnabled] = @UserEnabled AND [Email] LIKE @Email

Nested where conditions

If you need to construct complex where conditions with multiple AND/OR operators, use nested where conditions:

Note: You must use the new keyword to construct nested where conditions.

// Retrieves users named "Smith", whose first name is "Joe" or "John"
var nestedWhereQuery = UserInfoProvider.GetUsers()
    .WhereEquals("LastName", "Smith")
    .Where(new WhereCondition()
        .WhereEquals("FirstName", "Joe")
        .Or()
        .WhereEquals("FirstName", "John")
    );

DECLARE @LastName nvarchar(max) = N'Smith';
DECLARE @FirstName nvarchar(max) = N'Joe';
DECLARE @FirstName1 nvarchar(max) = N'John';

...

WHERE [LastName] = @LastName AND ([FirstName] = @FirstName OR [FirstName] = @FirstName1)

Retrieving data assigned to a particular site

Many Kentico objects that are stored in the database are related to a particular site. ObjectQuery allows you to filter results by site by providing a site ID or code name.

// Retrieves all users assigned to the current site
var siteQuery = UserInfoProvider.GetUsers()
    .OnSite(SiteContext.CurrentSiteID);

// Retrieves all users assigned to the Corporate site
var siteQuery = UserInfoProvider.GetUsers()
    .OnSite("CorporateSite");

Ordering query results (SQL ORDER BY)

ObjectQuery can also sort data. Use .OrderBy, .OrderByAscending, or .OrderByDescending.

var orderedQuery = UserInfoProvider.GetUsers()
    .WhereGreaterThan("UserCreated", DateTime.Now.AddDays(-7))
    .OrderByDescending("UserCreated");

This example retrieves users who registered or were created in the system during the past week. The results are in descending order.

Limiting the number of query results (SQL TOP N)

ObjectQuery can also retrieve only a specified number of results.

var topNQuery = ForumPostInfoProvider.GetForumPosts()
    .TopN(5)
    .OrderByDescending("PostTime");

This example retrieves the latest 5 forum posts with the newest post on top.

Joining multiple tables (SQL JOIN)

With ObjectQuery, you can combine data from two or more tables based on a common field.

var joinQuery = UserInfoProvider.GetUsers()
    .Source(sourceItem => sourceItem.Join<UserSettingsInfo>("UserID", "UserSettingsUserID"))
    .WhereEmpty("UserPassword");

This example retrieves users, who have not set a password, i.e., whose password is blank.

The code on the second line appends CMS_UserSettings table rows to the appropriate user records based on their ID. The code on the third line then selects only rows where the UserPassword is empty.

Joining 3 or more tables

You can chain together multiple Join methods to combine rows from 3 or more database tables.

Note: When you call the Join method for a query source, the left column parameter works with columns within the given query source table by default. When using multiple joins, we recommend that you explicitly specify both the table and column by adding a table name prefix to the left column name, for example: “CMS_User.UserID”

The following example joins together rows from 3 tables based on shared user IDs and returns the result as a DataSet.

using System.Data;
using CMS.Membership;
using CMS.Taxonomy;

...

DataSet data = UserInfoProvider.GetUsers()
    .Source(sourceItem => sourceItem.Join<UserSettingsInfo>("CMS_User.UserID", "UserSettingsUserID")
                                    .Join<CategoryInfo>("CMS_User.UserID", "CategoryUserID")
            )
    .Columns("UserID, UserName, UserURLReferrer, CategoryDisplayName")
    .Result;

Working with ObjectQuery results

ObjectQuery results are lazy-loaded. Lazy loading increases performance by executing queries only when you need to work with their results. Most of the examples on this page only constructed the proper SQL queries. The SQL queries are executed when you either enumerate the results using the foreach statement, or cast the query as a different type (for example a DataSet).

The system caches the loaded data, so if you work with the results after the query executed, the system will not perform any additional requests to the database.

The most common example of working with query results is iterating through them. Use a standard foreach loop.

var userQuery = UserInfoProvider.GetUsers();

foreach (UserInfo user in userQuery)
{
    // Do something with the UserInfo object
}

Reusing queries (mutability)

ObjectQuery instances are mutable by default. This means that any changes (method calls) made to existing instances also modify the original query.

If you wish to reuse an ObjectQuery instance without modifying the original, use one of the following approaches:

• Call the Immutable method for the original query. This ensures automatic cloning of the ObjectQuery instance when it is modified.
• If you want to leave a query mutable, you can call the Clone method to create a new instance which can then be modified without affecting the original.

using System.Linq;
using CMS.Membership;

...

// Creates an immutable query for loading users ordered by their full name
var userQuery = UserInfoProvider.GetUsers()
    .OrderBy("FullName")
    .Immutable();

// Gets a subset of users based on the original query
var enabledUserList = userQuery
    .WhereEquals("UserEnabled", 1)
    .ToList();

// Gets a list of users using the original unmodified query
var userList = userQuery.ToList();