处理QueryDSL中的可选参数

Question

我在SpringData中使用QueryDSL。我有表说，Employee和我创建实体类说，EmployeeEntity我写了以下服务方法

public EmployeeEntity getEmployees(String firstName, String lastName)
{
    QEmployeeEntity employee = QEmployeeEntity.employeeEntity;
    BooleanExpression query = null;
    if(firstName != null)
    {
        query = employee.firstName.eq(firstName);
    }
    if(lastName != null)
    {
        query = query.and(employee.lastName.eq(lastName)); // NPException if firstName is null as query will be NULL
    }
    return empployeeDAO.findAll(query);
}

如上所述，我评论了NPException。如何使用Spring数据在QueryDSL中使用QueryDSL作为可选参数？

谢谢 ：）

Answer 1

BooleanBuilder可以用作布尔表达式的动态构建器：

public EmployeeEntity getEmployees(String firstName, String lastName) {
    QEmployeeEntity employee = QEmployeeEntity.employeeEntity;
    BooleanBuilder where = new BooleanBuilder();
    if (firstName != null) {
        where.and(employee.firstName.eq(firstName));
    }
    if (lastName != null) {
        where.and(employee.lastName.eq(lastName));
    }
    return empployeeDAO.findAll(where);
}

Answer 2

BooleanBuilder很好。你也可以包装它并添加“可选”方法以避免if条件：

例如，对于“和”，您可以编写:(使用Java 8 lambdas）

public class WhereClauseBuilder implements Predicate, Cloneable
{
    private BooleanBuilder delegate;

    public WhereClauseBuilder()
    {
        this.delegate = new BooleanBuilder();
    }

    public WhereClauseBuilder(Predicate pPredicate)
    {
        this.delegate = new BooleanBuilder(pPredicate);
    }

    public WhereClauseBuilder and(Predicate right)
    {
        return new WhereClauseBuilder(delegate.and(right));
    }

    public <V> WhereClauseBuilder optionalAnd(@Nullable V pValue, LazyBooleanExpression pBooleanExpression)
    {
        return applyIfNotNull(pValue, this::and, pBooleanExpression);
    }

    private <V> WhereClauseBuilder applyIfNotNull(@Nullable V pValue, Function<Predicate, WhereClauseBuilder> pFunction, LazyBooleanExpression pBooleanExpression)
    {
        if (pValue != null)
        {
            return new WhereClauseBuilder(pFunction.apply(pBooleanExpression.get()));
        }

        return this;
    }
   }

    @FunctionalInterface
    public interface LazyBooleanExpression
    {
        BooleanExpression get();
    }

然后使用会更清洁：

public EmployeeEntity getEmployees(String firstName, String lastName) {
    QEmployeeEntity employee = QEmployeeEntity.employeeEntity;

    return empployeeDAO.findAll
    (
       new WhereClauseBuilder()
           .optionalAnd(firstName, () -> employee.firstName.eq(firstName))
           .optionalAnd(lastName, () -> employee.lastName.eq(lastName))
    );
}

也可以使用jdk的Optional类

Answer 3

实际上这是Java 101：检查null并初始化查询而不是连接谓词。所以像这样的辅助方法可以做到这一点：

private BooleanExpression createOrAnd(BooleanExpression left, BooleanExpression right) {
  return left == null ? right : left.and(right);
}

然后你可以简单地做：

BooleanExpression query = null;

if (firstName != null) {
  query = createOrAnd(query, employee.firstName.eq(firstName));
}

if (lastName != null) {
  query = createOrAnd(query, employee.lastName.eq(lastName));
}

…

请注意，我甚至在第一个子句中使用createOrAnd(…)只是为了保持一致性，并且如果您决定在firstName之前添加新子句，则不必调整该代码。

Answer 4

我遇到了同样的问题，这里有另一个版本的Timo Westkämper 使用accepted answer的Optional。

default Optional<Correlation> findOne(
        @Nonnull final String value, @Nullable final String environment,
        @Nullable final String application, @Nullable final String service) {
    final QSome Some = QSome.some;
    final BooleanBuilder builder = new BooleanBuilder();
    ofNullable(service).map(some.service::eq).map(builder::and);
    ofNullable(application).map(some.application::eq).map(builder::and);
    ofNullable(environment).map(some.environment::eq).map(builder::and);
    builder.and(some.value.eq(value));
    return findOne(builder);
}

Answer 5

根据你的需要，我会这样做

public List<EmployeeEntity> getEmployees(Optional<String> firstName, Optional<String> lastName)
{
    BooleanExpression queryPredicate =  QEmployeeEntity.employeeEntity.firstName.containsIgnoreCase(firstName.orElse("")).and(QEmployeeEntity.employeeEntity.lastName.containsIgnoreCase(lastName.orElse(""))); 
    return empployeeDAO.findAll(queryPredicate);
}

首先，你应该返回List的EmployeeEntity。其次，最好使用可选项而不是检查它的null，并且你可以传递从可选的Optional获得的Java 8的RequestParam值，如下所示：

@RequestMapping(value = "/query", method = RequestMethod.GET)
public ModelAndView queryEmployee(@RequestParam(value = "firstName", required = false) Optional<String> firstName, @RequestParam(value = "lastName", required = false) Optional<String> lastName) 
{
       List<EmployeeEntity> result =  getEmployees(firstName, lastName);    
            ....
}

而且一个非常重要的事情是在谓词中使用containsIgnoreCase函数：它比典型的like更好，因为它不区分大小写。

在我看来，你应该使用这样的方法：

@Controller
class UserController {

  @Autowired UserRepository repository;

  @RequestMapping(value = "/", method = RequestMethod.GET)
  String index(Model model, @QuerydslPredicate(root = User.class) Predicate predicate,    
          Pageable pageable, @RequestParam MultiValueMap<String, String> parameters) {

    model.addAttribute("users", repository.findAll(predicate, pageable));

    return "index";
  }
}

看看here。

Answer 6

如果你检查null的QueryDSL实现：

public BooleanExpression and(@Nullable Predicate right) {
    right = (Predicate) ExpressionUtils.extract(right);
    if (right != null) {
        return BooleanOperation.create(Ops.AND, mixin, right);
    } else {
        return this;
    }
}

这应该是你想要的。

Answer 7

这是处理可选参数的一种非常简单的方法，我在我的项目中使用它：

    public List<ResultEntity> findByOptionalsParams(String param1, Integer param2) {
    QResultEntity qResultEntity = QResultEntity.resultEntity;
    final JPQLQuery<ResultEntity> query = from(qResultEntity);
    if (!StringUtils.isEmpty(param1)) {
      query.where(qResultEntity.field1.like(Expressions.asString("%").concat(param1).concat("%")));
    }
    if (param2 != null) {
      query.where(qResultEntity.field2.eq(param2));
    }
    return query.fetch();
}