Record Sets Commentary

General:. Record Sets in Glee are like tables of structures in other languages. A record set is composed of two objects: (1) a sequence of records(which are sequences of fields) and (2) field list (naming fields within records). It can be viewed as a table with named columns. There are facilities for creating the record set; defining its fields; populating its records; adding, deleting, and renaming fields; replacing and deleting records; and retrieving by field, by record, or by combination of both. Glee record sets do not impose a discipline. They merely provide a mechanism for naming and thereby referring to elements of a record sequence. For example, you can put string data where numerics belong and the record set does not debate. Glee will, however, assure that there is a correspondence between the field names and the fields in all the records. On entry, it scans all data for conformance and rejects all or accepts all. Use of Record Sets can make programs more readable.





Create Record Set (#RS): The niladic operator "#RS" creates a record set with no fields and no records. You can assign this to a variable which can then be the target for populating the record set. This record set contains no fields and no records. It is simply an object with and empty field list object and record sequence containing no elements.




Add fields to new record set: You can add fields at any time. Glee checks to be sure the field your adding is not already part of the record set object. If it is, a diagnostic is given. If not, the field is appended to the field list for the record set. If the record set contains records, new items are appended to each record. These items are a null objects.




Add Records: Data records are added to record sets by assigning to an empty record set index. This is the same method we used for adding fields. When you append new records to the record set using null indexing (i.e. []) the field order of the record set is assumed. This can be obtained using the .fields property for the record set (e.g. rs.fields).




Rearranging and deleting fields in a record set: Record set fields are maintained in the order in which they are supplied. New fields are appended to the field list. If you want to change this order or remove fields, you do so by field indexing into the record set. This creats a new record set in the new order. You can then replace the existing record set with it. Record sets are just collections of pointers. However, when you rearrange fields, you are rearranging the elements of the record sequences as well. If the record set is very large, this is probably not a good idea. Records sets should probably not be allowed to grow to great size. They are intended for managing small tables of data.




Create with field list: It is common to create the record set with its initial complement of fields rather than to add fields later.




Get Fields: When you get information from a record set you are given a completely new record set. Typically you'll only be interested in the records part (presumably you already know everything about the fields part). See the next example for how to get just the records part.




The .recs and .fields properties: Typically when working with the data in the record set, you only want the "sequence of records" part. The ".recs" property returns this. If you want the field list part, the ".fields" returns that. These are not references. You can't change data in this result and expect it to change in the original record set.




Addressing: Addressing in record sets can be by record(s); by field(s); or by a combination as shown here. When using the combination specify the field(s) together (in the order you want) t the record number(s) (in the order you want). It doesn't matter which order you use.




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