从 MongoDB 返回的嵌套文档的 Java 8 Stream 实现

Question

我有一个嵌套文档的 MongoDB 集合，如下所示。我正在尝试读取 TestCase 对象中的标签。现在我的实现非常基本，有 4 个 for 循环。我是 java8 的新手，我想使用流或任何简单的方法来读取嵌套数据集。

class TestResults {
        public String ID;   
        DateTime timeStamp;
        List<TestCapability> testCapability;
}

class TestCapability {
        public String ID;   
        DateTime timeStamp;
        List<TestSuite> testSuite;
}

class TestSuite {
        public String ID;   
        DateTime timeStamp;
        List<TestCase> testCase;
}

class TestCase {
        public String ID;   
        DateTime timeStamp;
        List<TestSteps> testSteps;
        private Set<String> tags = new HashSet<>();
}

我当前的实现非常糟糕，如下

    for (TestResult testResult : testResults) {
        for (TestCapability capability : testResult.getTestCapabilities()) {
            for (TestSuite testSuite : capability.getTestSuites()){
                for (TestCase testCase : testSuite.getTestCases()) {
                    for (Feature feature : featureDetails) { 
                        if (testCase.getTags().contains(feature.getsNumber())){
                            testResultsAuditResponse.setsId(feature.getsId());
                            testResultsAuditResponse.setsNumber(feature.getsNumber());
                            testResultsAuditResponse.setsName(feature.getsName());
                            testResultsAuditResponse.setsStatus(feature.getsStatus());
                        }
                    }
                }
            }
        }
    }

Answer 1

答案是使用 flatMap:

testResults.stream()
    .map(TestResult::getTestCapabilities).flatMap(Collection::stream)
    .map(TestCapability::getTestSuites).flatMap(Collection::stream)
    .map(TestSuite::getTestCases).flatMap(Collection::stream)
    .forEach(testCase -> {
        featureDetails.stream()
            .filter(feature -> testCase.getTags().contains(feature.getsNumber()))
            .map(Feature::getsId)
            .forEach(testResultsAuditResponse::setsId);
    });