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Appendix A. Enumeration Extension Methods
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LINQ Reporting Engine enables you to perform common manipulations on a sequential data through the engine’s built-in extension methods for Iterable. These extension methods mimic some extension methods of IEnumerable<T> providing the same signatures and behavior features. Thus, you can group, sort, and perform other sequential data manipulations in template expressions in a common way.
The following table describes these built-in extension methods. The following notation conventions are used within the table:
Selectorstands for a lambda function returning a value and taking an enumeration item as its single argument. See “Using Lambda Functions” for more information.ComparableSelectorstands forSelectorreturning Comparable.EnumerationSelectorstands forSelectorreturningIterable.Predicatestands forSelectorreturning aBooleanvalue.
Examples in the following table are given using persons and otherPersons, enumerations of instances of the Person class that is defined as follows.
public class Person
{
public String getName() { ... }
public int getAge() { ... }
public Iterable<Person> getChildren() { ... }
...
}
| Extension Method | Examples and Notes |
|---|---|
all(Predicate) |
|
any() |
|
any(Predicate) |
|
average(Selector) |
|
concat(Iterable) |
|
contains(Object) |
|
count() |
|
count(Predicate) |
|
distinct() |
|
elementAt(int) |
|
elementAtOrDefault(int) |
|
first() |
|
first(Predicate) |
|
firstOrDefault() |
|
firstOrDefault(Predicate) |
|
groupBy(Selector) |
Key field. You can treat a group itself as an enumeration of items that the group contains. |
last() |
|
last(Predicate) |
|
lastOrDefault() |
|
lastOrDefault(Predicate) |
|
max(ComparableSelector) |
|
min(ComparableSelector) |
|
orderBy(ComparableSelector) |
- thenBy(ComparableSelector) - thenByDescending(ComparableSelector) |
orderByDescending(ComparableSelector) |
|
select(Selector) |
|
selectMany(EnumerationSelector) |
|
single() |
|
single(Predicate) |
|
singleOrDefault() |
|
singleOrDefault(Predicate) |
|
skip(int) |
|
skipWhile(Predicate) |
|
sum(Selector) |
|
take(int) |
|
takeWhile(Predicate) |
|
union(Iterable) |
|
where(Predicate) |
|
FAQ
-
Q: How can I obtain the index of the current item inside a
foreachloop in a template?
A: Use the built‑inindexvariable that the LINQ Reporting Engine provides for each iteration. Inside theforeachtag you can write<<#= index>>to output the zero‑based position of the current element. -
Q: Is there a way to access the previous element while iterating over a collection?
A: The engine does not expose a directprevious()method. A common workaround is to useskip(1)together withfirst()on a sliced collection, e.g.,persons.skip(1).first()gives the element after the first one, which you can compare with the current index. -
Q: How do I group items by a calculated key, such as age, and then iterate over each group?
A: Use thegroupByextension method. Example:persons.groupBy(p => p.getAge())returns a collection of groups. Inside the template you can iterate:<<foreach [group in persons.groupBy(p => p.getAge())]>> Age: <<group.Key>> Count: <<group.count()>> <<endforeach>>. -
Q: What extension methods should I use to sort a collection by multiple fields?
A: First applyorderBy(ororderByDescending) with the primary key, then chainthenByorthenByDescendingfor secondary keys. Example:persons.orderBy(p => p.getAge()).thenByDescending(p => p.getName()).thenBy(p => p.getChildren().count()). -
Q: How can I check whether any element in a collection satisfies a condition?
A: Use theany(Predicate)method. Example:persons.any(p => p.getAge() > 65)returnstrueif at least one person is older than 65, otherwisefalse.