 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
 | There 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.
Lazy loading query
The evaluation of a lazy loading Query's children is done automatically if no local children exist yet, otherwise evaluation has to be triggered manually to prevent excessive server calls. In the case of an Offline Query the evaluation happens despite the existence of local children.
Usage of DatabaseViews
It is also possible to define a Database View and use this View for the evaluation of Queries (see VirtualContentClass).