如何检查该值是否等于列表中的至少一个字段？

Question

I have method like this:

for (String fieldName : fieldArray) {
        Query query = new Query();
        query.addCriteria(Criteria.where("data." + fieldName).is("some_constant"));
        if (mongoTemplate.find(query, DataPoint.class).size() > 0) {
            return true;
      }
}
return false;

This code looks inefficient because it access to db so much how fieldArray size.

Is there way to replace it using single query?

Answer 1

Why not using Criteria::in method and pass a List instead of Iterate over all the element and check element by element, I think you need just this :

query.addCriteria(
  Criteria.where("data." + fieldName).in(fieldArray)
);

---

Beside the comment of @Veeram the first way will work if you want to check if one field can hold one of the values in your list, but it seems that your problem is different, what i understand, you want to check a value exit in multiple fields, to solve this issue you can use :

//Consider you want to check in multiple fields
List<String> fieldArray = Arrays.asList("field1", "field2", "field3");

// First you have to create a list of Criteria (multiple conditions)
List<Criteria> listOfCondition = new ArrayList<>();
for (String fieldName : fieldArray) {
    listOfCondition.add(
            Criteria.where("data." + fieldName).is("some_constant")
    );
}

//The add them to the query.
Criteria criteria = new Criteria();
for (Criteria c : listOfCondition) {
    criteria = criteria.orOperator(c);
}
Query query = new Query();
query.addCriteria(criteria);
//Then execute your query just one time

---

With streams you can use :

List<String> fieldArray = Arrays.asList("field1", "field2", "field3");
Criteria principaleCriteria = new Criteria();
fieldArray.stream()
        .map(fieldName -> Criteria.where("data." + fieldName).is("some_constant"))
        .forEach(criteria -> principaleCriteria.orOperator(criteria));
Query query = new Query();
query.addCriteria(principaleCriteria);
return mongoTemplate.count(query, DataPoint.class) > 0;

Although technically correct when you run the code you will get

org.springframework.data.mongodb.InvalidMongoDbApiUsageException: Due to limitations of the com.mongodb.BasicDBObject, you can't add a second '$or' expression specified as '$or : [ { "data.field2" : "some_constant"}]'. Criteria already contains '$or : [ { "data.field1" : "some_constant"}]'.

Mongodb compliant code:

List<String> fieldArray = Arrays.asList("field1", "field2", "field3");
Criteria principaleCriteria = new Criteria();
List<Criteria> orExpressions = fieldArray.stream()
                .map(fieldName -> Criteria.where("data." + fieldName).is("some_constant"))
                .collect(toList());
Query query = new Query();
        query.addCriteria(principaleCriteria.orOperator(orExpressions.toArray(new Criteria[orExpressions.size()])));

Outputs:

{ "$or" : [ { "data.field1" : "some_constant"} , { "data.field2" : "some_constant"} , { "data.field3" : "some_constant"}]}

Answer 2

Seems to me that you could use public Criteria orOperator(Criteria... criteria)

It should be something like :

List<Criteria> criterias = new ArrayList<>();
for (String fieldName : fieldArray) {
    //Create the criterias like you want
    criterias.add(Criteria.where("data." + fieldName).is("some_constant"));
}

Query query = new Query(
    new Criteria().orOperator(
        criterias.toArray( //convert the list into an Criteria[] for the varargs parameter
            new Criteria[criterias.size()]
        )
    )
);

This will create a list of Criteria that will be used to generate an Criteria instance that will be valid if one criteria is valid (OR operation, one true is enough).