Difference between revisions of "QUERY"

Revision as of 16:45, 9 December 2013

Query
Name	QUERY
Namespace	System.Query Custom.Query
Internal Name	Query
TypeString	{{{typestring}}}
RuntimeType	{{{runtimetype}}}
Purpose	Configure queries
Version	2+

Basics

In UBIK, queries are used for fetching a list of ContentClasses from the database. Queries use data base mechanism for perfomant data access and will deliver a list of objects of a certain Metaclass. Queries can be used in different scenarios:

• data fetching (n records)
• finding a single or a set of recordset(s)
• used as definition of root nodes in a View

Query, QueryItem

A Query is defined for a single MetaClass. The MetaClass is defined by a Referenceproperty FILTEROBJECT. A Query will deliver ContentClasses(instances) of the defined MetaClass. A Query holds a list of QueryItems. A single QueryItem defines a single filter rule for the evaluation of the result collection:

• OPERATOR

e.g. “=”

• LIKECOMPARISON

is the given item a “LIKE” filter criteria (wildcard is added to the filtervalue)

• FILTERVALUE

the value the objects are compared to

• ISNULL

searched for NULL values

• LOGICALAND

is there a logical AND relation between the given QueryItem and its predecessor (TRUE) or an OR relation (false)

Relation between Query and Items

The correspondence between Queries and its items is created and stored by a relationship QUERYRELATION. Therefore a single QueryItem can be used several times for different Queries.

Content queries

We often face the need to fetch a list of objects meeting arbitary criteria, for example for

• scanning of ID markers (QR-Code, Barcode, …)
• show objects from deeper hierarchy levels

Storing of data permanently on the device would need too much resources, hence we load the objects from server on demand. Characteristics of a content query are

• derivative from QUERY classified as SYSCLS_QUERY marks instances as content queries
• Related to instances via relations
• Placed in view hierarchy defined via view items
• Require context scopes on client side

Configuration of a content query requies

• Set filter object (FILTEROBJECT) similar as for other query
• Create a proper relation
• Create a query view item and set the instance as QUERY
• Create a relation view item and set the according default MetaClass and relation
• Create and relate a query context scope and set the instance as QUERY
• For the scope define the MetaProperties, which should be available as filter criteria on the client. Without appropriate query item, equality is used as filter operator (=)

Usage of DatabaseViews

It is also possible to define a Database View and use this View for the evaluation of Queries (see VirtualContentClass).