Collections - griffio/griffio.github.io GitHub Wiki

Collections

CollQueryFactory

com.mysema.query.collections

Query entities that are generated can be used with a CollQueryFactory to replace this Mundane Java code that maps an input collection to an output collection.

Before

private List<String> uniqueSalaryNames(Collection<EmployeeSalary> employeeSalaries) {
    Set<String> result = Sets.newHashSet();
        for (EmployeeSalary salary : employeeSalaries) {
            for (SalaryDetail detail : salary.getSalaryDetails()) {
                if (RelevantSalaryUtil.isSalaryRelevant(detail.getSalaryName())) {
                    result.add(detail.getSalaryName());
                }
            }
        }
    return newArrayList(result);
}

After

List<String> uniqueSalaryNames = CollQueryFactory
    .from(QEmployeeSalary.employeeSalary, employeeSalary)
    .innerJoin(QEmployeeSalary.employeeSalary.salaryDetail, QSalaryDetail.salaryDetail)
    .where(QSalaryDetail.salaryDetail.isSalaryRelevant())
    .distinct()
    .list(QEmployeeSalary.employeeSalary.salaryName);

Aggregate or 'fold' a collection using Mundane Java. Even the Guava library doesn't advocate higher-order functional programming using Java.

Before

public BigDecimal sum(List<SalaryDetail> salaryDetails) {
   BigDecimal sum = BigDecimal.ZERO;
   for (SalaryDetail salaryDetail : salaryDetails) {
      sum = sum.add(salaryDetail.getSalary());
   }
   return sum;
};

After

BigDecimal sum = CollQueryFactory
   .from(QSalaryDetail.salaryDetail, salaryDetails)
   .singleResult(QSalaryDetail.salaryDetail.salary.sum());

ResultTransformer

com.mysema.query

A post-processor transformer for aggregation that works with com.mysema.query.group.* classes.

Takes a collection and returns a collection containing a new projection of the aggregate for each group. Here, multiple salaries with the same name will be grouped into a new element containing the sum total of the group.

List<SalaryDetail> aggregatedSalaries = CollQueryFactory.from(QSalaryDetail.salaryDetail, salaryDetails)
    .transform(GroupBy.groupBy(QSalaryDetail.salaryDetail.salaryName)
    .list(QSalaryDetail.create(QSalaryDetail.salaryDetail.salaryName,    
        GroupBy.sum(QSalaryDetail.salaryDetail.salary))));
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