The OCLOperator PSEvalTuples makes it possible to use oclPS in any OCL expression. Using this, you can "reach into" the database from OCL and action-language (EAL).

Expression template:

SomeClass.PSEvalTuples(<ps-expression>,maxfetch,offset,<dependon>) 

Note! PSEvalTuples doesn't subscribe to sets from DB. To make the operator auto-updating, provide an expression in "dependon" that, when changed, should also rerun the PSEvalTuples expression. This can, for example, be a timer.

Example:

Consultant.PSEvalTuples(self.Assignments->select(a|a.Active)->collect(a|a,a.Consultant,a.BilledHours->select(bh|bh.WorkDate>vTheStartDate).Hours->sum),  100, 0, vTheStartDate) 

The result type is a Tuple.

The above expression reaches into the database for all Consultants, takes the active assignments, sums the BilledHours that have been reported after vTheStartDate and returns a list of tuples of type {Assignment,Consultant,Part1} where part1 will be the sum of hours.

Note on limitations: OCL is a more expressive language than SQL. This leads to situations where something that is easy to express in OCL MAY NOT be correctly translated to an equivalent SQL-statement. We know that performing multiple aggregating functions like sum, min, max, avg, and count(*) (in OCL, it will be ->minvalue, ->maxvalue, ->average, ->size) in the same tuple for different sets of data will not yield the expected results. Always do a sanity check of the numbers returned from a new expression and test it to verify its efficacy. Example of expression given wrong answer: ->collect(x|x,x.Name,x.Something->select(goodone).Value->sum,x.Something->select(badone).Value->sum ) workaround - split it in two, one expression per aggregation,

Always remember that your SQL-server might also need indexes and other performance settings to execute your expression efficiently.

See also: Sqlpassthrough, PSEvalValue, PSEval