解析Spring Boot中MongoDB排序字段-1L的含义与应用

import com.mongodb.client.model.Aggregates;
import com.mongodb.client.model.Filters;
import org.bson.Document;
import org.bson.conversions.Bson;
import org.bson.types.ObjectId;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class MovieRepository {

    // 假设 moviesCollection 是一个 MongoCollection<Document> 实例

    public Document getMovie(String movieId) {
        // ... (省略id校验)

        List<Bson> pipeline = new ArrayList<>();
        // 匹配阶段，查找电影
        Bson match = Aggregates.match(Filters.eq("_id", new ObjectId(movieId)));
        pipeline.add(match);

        // 查找并关联评论
        pipeline.addAll(Arrays.asList(new Document("$lookup",
                new Document("from", "comments")
                        .append("let",
                                new Document("id", "$_id"))
                        .append("pipeline", Arrays.asList(new Document("$match",
                                        new Document("$expr",
                                                new Document("$eq", Arrays.asList("$movie_id", "$$id")))),
                                new Document("$sort",
                                        new Document("date", -1L)))) // 这里的 -1L 是关注点
                        .append("as", "comments"))));

        // 执行聚合并获取第一个结果
        // Document movie = moviesCollection.aggregate(pipeline).first();

        // return movie;
        return null; // 示例代码，实际应返回查询结果
    }
}

import org.junit.Assert;
import org.junit.Test;
import org.bson.Document;

import java.util.List;

public class MovieRepositoryTest {

    // 假设 dao 是 MovieRepository 的一个实例
    private MovieRepository dao = new MovieRepository(); // 实际应通过依赖注入或实例化

    @SuppressWarnings("unchecked")
    @Test
    public void testGetMovieComments() {
        String movieId = "573a13b5f29313caabd42c2f";
        Document movieDocument = dao.getMovie(movieId); // 调用上面定义的 getMovie 方法
        Assert.assertNotNull("Should not return null. Check getMovie()", movieDocument);

        List<Document> commentDocs = (List<Document>) movieDocument.get("comments");
        int expectedSize = 147;
        Assert.assertEquals(
            "Comments list size does not match expected", expectedSize, commentDocs.size());

        String expectedName = "Arya Stark";
        Assert.assertEquals(
            "Expected `name` field does match: check your " + "getMovie() comments sort order.",
            expectedName,
            commentDocs.get(1).getString("name")); // 验证排序结果
    }
}