Difference between revisions of "QUERY"
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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 [[QUERYITEM|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 [[QUERYITEM|QueryItems]]. | ||
Revision as of 10:47, 24 March 2015
 Query |
|
|---|---|
| Name | QUERY |
| Namespace | System.Query Custom.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! |
Contents
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.
Relation between Query and Items
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.
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).
