Order a selection (case sensitive)
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WSupported on Windows
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USupported on Unix
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VSupported on OpenVMS
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NSupported in Synergy .NET
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namespace Synergex.SynergyDE.Select public class OrderBy
The OrderBy class is a collection of static methods for ordering a selection, either by key or non-key fields, when the selection is created. The AscendingKey() and DescendingKey() methods specify the order in which a selected key is traversed, thereby affecting the order of the final output, where no post-selection ordering is done. The Ascending() and Descending() methods enable you to order selected records by any field(s) regardless of whether they are defined keys, where the ordering process takes place after the entire selection has been done.
public static varargs Ascending(field1, ...), @OrderBy
Declares a list of fields (MISMATCH n), separated by commas, by which the selected records will be sorted in ascending order upon being returned.
public static AscendingKey(krf), @OrderBy
Processes the selection in ascending order by key of reference (n).
public static varargs Descending(field1, ...), @OrderBy
Declares a list of fields (MISMATCH n), separated by commas, by which the selected records will be sorted in descending order upon being returned.
public static DescendingKey(krf), @OrderBy
Processes the selection in descending order by key of reference (n).
The logical and operator (&& or .AND.) is supported and is equivalent to its Synergy counterpart. See Expressions for more information about this operator.
Discussion
The AscendingKey() and DescendingKey() methods specify the key of reference for the Where object selection if the key of reference has not been explicitly specified by Where.Keynum(). If a key of reference is specified by both Where.Keynum() and either AscendingKey() or DescendingKey(), it must be the same key or an InvalidOperationException or $ERR_INVOPER error (“Keynum(#) doesn’t match OrderBy key #”) will be generated. If the specified key of reference is a segmented key, and the segments are individually ordered differently, the order is determined by the key optimization level. If no optimization occurs, the order is determined by the first key segment. (See Optimization and ordering for ISAM files for more detailed information.)
When Ascending() or Descending() is used, the entire selection is read from the specified file when the AlphaEnumerator object is created (on Select.GetEnumerator() or FOREACH). Changes to the file after making the selection may not be reflected in the records retrieved, especially if a record that matches the selection criteria is updated or inserted.
The fields specified by Ascending() and Descending() must be in the record specified in the From class object. If they are not, an InvalidOperationException or $ERR_INVOPER error (“Field reference not entirely part of specified record”) will be generated at runtime. When used with a JoinSelect, the fields can be from any record in any of the joined From objects and can be specified in any order. However, specified fields must have unambiguous names, so if fields in different records have the same name, you must include the record name in addition to the field name.
You can combine multiple fields in your sort criteria using the .AND. operator. For example,
sobj = new Select(from, wobj, & OrderBy.Descending(fld1).and.OrderBy.Ascending(fld2))
OrderBy is case sensitive (unless you’re sorting by a NOCASE key in the file). If you need case-insensitive ordering of records, use Synergex.SynergyDE.Select.NoCaseOrderBy. OrderBy and NoCaseOrderBy can be combined if only some fields require case-insensitivity.
You cannot combine OrderBy and GroupBy in the same Select statement.
See also
