我在解析服务器上找不到以下问题的解决方案。它等效于在SQL中使用JOIN,但是因为Parse Server使用NoSQL,所以解决方案不是联接。
问题;报告屏幕显示查询结果。但是需要从另一个类中查找一个字段,并替换为另一个类中的字段。
我只能通过使用两个单独的嵌套查询来解决此问题,但这是有效的方式。您能告诉我如何在单个查询中或更有效地执行以下操作吗?
//get query result from database
ParseQuery<ParseObject> query = ParseQuery.getQuery("access");
query.whereStartsWith("tokenid", "prefix");
query.findInBackground(new FindCallback<ParseObject>() {
@Override
public void done(List<ParseObject> objects, ParseException e) {
for (int i=0; i<objects.size(); i++) {
String reportField1 = objects.get(i).getString("name");
String lookup = objects.get(i).getString("cityID");
//start the second query
ParseQuery<ParseObject> query2 = ParseQuery.getQuery("cities");
query2.whereEqualTo("cityID", lookup);
query2.getFirstInBackground(new GetCallback<ParseObject>() {
@Override
public void done(ParseObject object, ParseException e) {
String reportField2 = object.getString("cityname");
}
});
}
}
});
您要查找的在Parse中称为pointer
。代替将cityID
存储在access
对象上,而存储指向cities
对象的指针并将其包含在查询中。
这里是Android guide的示例
ParseQuery<ParseObject> query = ParseQuery.getQuery("Comment");
// Retrieve the most recent ones
query.orderByDescending("createdAt");
// Only retrieve the last ten
query.setLimit(10);
// Include the post data with each comment
query.include("post");
query.findInBackground(new FindCallback<ParseObject>() {
public void done(List<ParseObject> commentList, ParseException e) {
// commentList now contains the last ten comments, and the "post"
// field has been populated. For example:
for (ParseObject comment : commentList) {
// This does not require a network access.
ParseObject post = comment.getParseObject("post");
Log.d("post", "retrieved a related post");
}
}
});
通过将指针存储在access
对象上,只需将其包含在查询中就可以获取相应的cities
对象。