content== Basics == Queries are used for fetching a list of objects from the database. Queries will use data base mechanism for perfomant data access. Queries 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 objects (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:* OPERATORe.g. “=”* LIKECOMPARISONis the given item a “LIKE” filter criteria (wildcard is added to the filtervalue) * FILTERVALUEthe value the objects are compared to * ISNULLsearched for NULL values* LOGICALANDis 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. == Usage of DatabaseViews == It is also possible to define a Database View and use this View for the evaluation of Queries (see [[VirtualContentClass]]).
[[Category:UBIK]][[Category:How to...]]
