Conditions of Record Display and Insertion
Introduction
Priority allows for two types of condition:
- a simple query condition, which restrict the records from the base table that can be retrieved into the form
- an Assign condition, which both restricts record display in the form and assigns the designated value to new records.
To specify a condition (regardless of type), use the Expression/Condition column of the Form Column Extension form (a sub-level of Form Columns). If it is too long to fit in that column, continue in the sub-level form.
Once the Form Column Extension form is exited, a check mark appears in the Expression/Condition column of its upper-level form, Form Columns. This flag makes it easy to find any form column with a condition.
Query Condition — Record Display
Query conditions restrict the records from the base table that can be accessed by the form in question. The condition must begin with a comparative operator (<, >, <=, >=, <>, =). Only records that comply with the prescribed condition will appear in the form.
Of course, users can add their own query conditions from within the form. Yet, whereas user stipulations change for each data retrieval (in keeping with the current situation), the predefined query conditions will always apply.
Example: To restrict the display of records in the WARHSBAL form to parts with actual balances in the warehouse, the following condition would be written for the TBALANCE column: >0. This condition should be written in any form that displays such balances. Hence, while the WARHSBAL table will include records with a balance of 0, only those records which meet the condition will appear in each of the forms.
As mentioned earlier, you should also use a simple query condition to link a query sub-level to its upper-level form. For instance, the condition linking a balance to its respective warehouse (=:WAREHOUSES.WARHS) restricts displayed balances to those for this particular warehouse. Without this restriction, balances for all warehouses would appear.
You include the operator (=) in this condition so that the user can delete records from the upper-level form even though records appear in the sub-level. The reason for this usage is that the built-in delete triggers do not allow the deletion of any records in an upper-level form when there are records with assigned values in the sub-level form. As opposed to Assign conditions, which assign values into each record in the sub-level, a simple query condition does not. Hence, deletion will not be blocked.
Assign Condition — Record Display and Insertion
An Assign condition is distinguished from a simple query condition in that no comparative operator is used. This type of condition not only restricts record display in the form to those records that hold a certain value, but also assigns that value to each new record. You are already familiar with one Assign condition — the one that links an updatable sub-level form to its upper-level (e.g., ORDERS.ORD). This condition, written in this case for the ORD column of the ORDERITEMS form, has a two-fold effect:
- It assigns an internal value (the value of ORD in the ORDERS form) to the ORD column of the ORDERITEMS form, whenever a new record is added.
- It restricts record display to those ordered items which contain that value in their ORD column.
Example: All order items in order 0998 will receive a value of “13” in their ORD column, whereas all items in order 1010 will receive an internal value of “22.” Consequently, the former set of ordered goods will appear in the ORDERITEMS form under order 0998, while the latter set will appear under order 1010.
Another use of an Assign condition is to distinguish between data records that are stored in the same table but displayed in different forms.
Example: Consider the following forms, all based on the DOCUMENTS table: Customer Shipments (DOCUMENTS_D), Goods Receiving Vouchers (DOCUMENTS_P) and Warehouse Transfers (DOCUMENTS_T). The records in these three forms are distinguished by their type (D for shipment, P for GRV and T for transfer). Thus, for example, the condition ‘D’ is written for the TYPE column of the DOCUMENTS_D form. Consequently, whenever a new record is inserted in the form, the hidden TYPE column is automatically assigned a value of D. Moreover, data retrieval will only retrieve records from the DOCUMENTS table that have a type of D. Similar conditions are written for the TYPE columns of DOCUMENTS_P and DOCUMENTS_T (P and T, respectively).