如何在Java中使用QueryDSL、Spring-Data、MongoDB创建嵌入式谓词

我来帮你搞定这个嵌套文档的QueryDSL谓词构建问题～首先得先对应你的Mongo文档结构，定义好实体类和QueryDSL的Q类（如果用了Spring Data MongoDB的QueryDSL支持，这些Q类会自动生成），大概结构如下：

// Rule实体
@Document
public class Rule {
    @Id
    private String id;
    private String name;
    private List<ExpressionGroup> expressionGroups;
    // getter/setter
}

// ExpressionGroup实体
public class ExpressionGroup {
    private String type;
    private List<Expression> expressions;
    // getter/setter
}

// Expression实体
public class Expression {
    private String name;
    private List<String> values;
    // getter/setter
}

// 自动生成的Q类示例
public class QRule extends EntityPathBase<Rule> {
    public static final QRule rule = new QRule("rule");
    public final StringPath id = createString("id");
    public final StringPath name = createString("name");
    public final ListPath<ExpressionGroup, QExpressionGroup> expressionGroups = this.<ExpressionGroup, QExpressionGroup>createList("expressionGroups", ExpressionGroup.class, QExpressionGroup.class, PathInits.DIRECT2);
}

public class QExpressionGroup extends EntityPathBase<ExpressionGroup> {
    public static final QExpressionGroup expressionGroup = new QExpressionGroup("expressionGroup");
    public final StringPath type = createString("type");
    public final ListPath<Expression, QExpression> expressions = this.<Expression, QExpression>createList("expressions", Expression.class, QExpression.class, PathInits.DIRECT2);
}

public class QExpression extends EntityPathBase<Expression> {
    public static final QExpression expression = new QExpression("expression");
    public final StringPath name = createString("name");
    public final ListPath<String, StringPath> values = this.<String, StringPath>createList("values", String.class, StringPath.class, PathInits.DIRECT2);
}

接下来针对不同的查询需求，构建对应的谓词：

1. 查询包含特定name和value的Expression #

比如要找所有expressions中存在name="name1"且包含value="VAL1"的Rule：

// 获取Q类实例
QRule qRule = QRule.rule;

// 构建谓词：匹配expressionGroups数组中任意一个元素，其expressions数组中任意一个元素满足name和value条件
Predicate predicate = qRule.expressionGroups.any()
        .expressions.any()
        .name.eq("name1")
        .and(qRule.expressionGroups.any()
                .expressions.any()
                .values.contains("VAL1"));

// 执行查询
List<Rule> rules = ruleRepository.findAll(predicate);

2. 按ExpressionGroup的Type筛选后查询表达式 #

比如要找type="WHEN"的ExpressionGroup下，存在name="name2"的Expression的Rule：

QRule qRule = QRule.rule;

// 用lambda写法让嵌套逻辑更清晰
Predicate predicate = qRule.expressionGroups.any(group -> 
        group.type.eq("WHEN")
        .and(group.expressions.any(expr -> expr.name.eq("name2")))
);

List<Rule> rules = ruleRepository.findAll(predicate);

3. 多条件组合查询 #

比如要同时满足：

• Rule的name包含"test"
• 存在type为"FOR"的ExpressionGroup，且其中有expression的name是"name3"且values包含"VAL6"

QRule qRule = QRule.rule;

Predicate predicate = qRule.name.contains("test")
        .and(qRule.expressionGroups.any(group -> 
                group.type.eq("FOR")
                .and(group.expressions.any(expr -> 
                        expr.name.eq("name3")
                        .and(expr.values.contains("VAL6"))
                ))
        ));

List<Rule> rules = ruleRepository.findAll(predicate);

关键注意点 #

• 针对MongoDB的数组类型，QueryDSL用any()方法来匹配数组中的任意一个元素满足条件
• 嵌套数组需要逐层用any()穿透，lambda写法能让复杂嵌套逻辑更易读
• 如果需要匹配数组中的所有元素都满足条件，可以用all()方法（不过你的场景大概率用any()更多）

内容的提问来源于stack exchange，提问作者user2112716