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QUERY


Revision as of 16:40, 3 December 2019 by NWE (Talk | contribs)

IC METACLASS.gif Query
Name QUERY
Namespace System.Query
Internal Name SystemObjects.QUERY
TypeString UBIK.Kernel.MetaClass
RuntimeType UBIK.Kernel.Query
Purpose Configure queries
Version 2+

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
IC Hint square.pngThere are specific methods available for this type!

Query and QueryItems

A Query is defined for a single MetaClass, where the MetaClass is defined in the property FILTEROBJECT. Once a query is evaluated it will deliver a list of objects of type ContentClasses (instances), filtered as defined by its QueryItems. The correspondence between Queries and its items is created and stored by a relationship SYSREL QUERY. Therefore a single QueryItem can be used several times for different Queries.

The "FILTEROBJECT" of a query describes the target MetaClass to find instances of. E.g., if I want to find pumps, a MetaClass "MC_PUMP" can be used as filter target. The query items of a query describe filters for property values. E.g., a query item could specify that only objects with a value larger than "12" in the "VOLTAGE" MetaProperty should be retrieved. Multiple query items can be connected logically (AND/OR) so all of them or just some (or one) of them need to match.

Content query

Objects can be loaded on demand from the server, as storing a huge amount of data permanently on the device would need too much resources. A content query is a Query instance classified as SYSCLS QUERY and can be related to other content objects. For being shown in the View hierarchy it is necessary to create a QueryViewItem for the query object itself. Further on, for being published to the client a Query Scopes has to be created and added to the ACM.

The result of the query depends on the network connection and the UBIK® sync mode and follows the same rules as Searching for objects by Optical codes.

Scan query

Objects can be searched by optical codes (e.g. Barcode, QR code) using a scan query.

See detailed articles on How to prepare the object and How to find objects on the client.

Usage of DatabaseViews

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

See also