Hi all,
Over the years, I’ve worked on an class for doing ad hoc queries. This class
has gotten better and better. At first, the API of this class and some
implementation details were not ready for public consumption in my opinion.
However, recently I took the time to polish the code as much as possible and if
I can get my employer's approval I would like to contribute this code to
project Wonder which has given us so much in return during the years.
Here is a preview of its functionality. Please let me know if you guys think
this would be a useful contribution.
ERXQuery.java
This class has a fluent API that mimics a select statement:
NSArray<NSDictionary<String,Object>> records =
ERXQuery.create()
.select (keys)
.from (entity)
.where (qualifier)
.groupBy (groupings)
.having (havingQualifier)
.orderBy (sortings)
.fetch();
Overview
ERXQuery allows you to use EOF constructs (EOQualifiers, EOAttributes,
EOSortOrdering, EOAttribute names, relationships, etc.) to create queries of
the form:
SELECT ...
FROM ...
WHERE ...
GROUP BY ...
HAVING ...
ORDER BY ...
Using Ad Hoc Attributes
You may use the ERXAdHocAttributes class to easily create ad hoc attributes to
use with your query. For example, the code below creates two ad hoc
EOAttributes. An ad hoc attribute is an EOAttribute that is not physically
attached to an entity and that has a definition. They are useful for
aggregating other attributes. The definition of the attribute can reference
relationships and attributes as shown below.
// Using a single query against the order entity, count the number of
// orders and line items that match the qualifier.
ERXAdHocAttributes attributes = ERXAdHocAttributes.create(orderEntity)
.add("itemCount", "COUNT(DISTINCT lineItems.lineItemID)", "intNumber")
.add("orderCount", "COUNT(DISTINCT orderID)", "intNumber");
NSDictionary<String,Object> row =
ERXQuery.create()
.select (attributes)
.from (orderEntity)
.where (qualifier)
.fetch()
.lastObject();
int orderCount = ((Number) row.objectForKey("orderCount")).intValue();
int itemCount = ((Number) row.objectForKey("itemCount")).intValue();
Fetching into a Custom Record Class
You can also fetch using a custom class of your choice, i.e. Foo, as shown
below:
// Using java >= 8 is easy with a lambda expression
NSArray<Foo> objs = query.fetch(editingContext, (ec, row) -> new Foo(ec, row));
// Using java < 8 you must provide a RecordConstructor
ERXQuery.RecordConstructor<Foo> recordConstructor =
new ERXQuery.RecordConstructor<Foo> {
@Override
public Foo constructRecord(EOEditingContext ec, NSMutableDictionary row)
{
return new Foo(ec, row);
}
};
NSArray objs = query.fetch(editingContext, recordConstructor);
Author: Ricardo J. Parada _______________________________________________
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