How to query nested objects

Question

I have a problem when querying mongoDB with nested objects notation   db messages find    headers     From   reservations marriott com        count   0 db messages find     headers From    reservations marriott com       count   5   I can t see what I am doing wrong  I am expecting nested object notation to return the same result as the dot notation query  Where am I wrong

User · Accepted Answer

db messages find    headers     From   reservations marriott com         This queries for documents where headers equals   From         i e  contains no other fields     db messages find     headers From    reservations marriott com        This only looks at the headers From field  not affected by other fields contained in  or missing from  headers     Dot-notation docs

User · Answer

Since there is a lot of confusion about queries MongoDB collection with sub-documents  I thought its worth to explain the above answers with examples   First I have inserted only two objects in the collection namely  message as    gt  db messages find   pretty           id    ObjectId  5cce8e417d2e7b3fe9c93c32         headers               From     reservations marriott com                  id    ObjectId  5cce8eb97d2e7b3fe9c93c33         headers               From     reservations marriott com            To     kprasad iitd gmail com           gt       So what is the result of query  db messages find  headers   From   reservations marriott com       count     It should be one because these queries for documents where headers equal to the object  From   reservations marriott com    only i e  contains no other fields or we should specify the entire sub-document as the value of a field    So as per the answer from  Edmondo1984          Equality matches within sub-documents select documents if the subdocument matches exactly the specified sub-document  including the field order       From the above statements  what is the below query result should be    gt  db messages find  headers   To   kprasad iitd gmail com   From   reservations marriott com       count   0   And what if we will change the order of From and To i e same as sub-documents of second documents    gt  db messages find  headers   From   reservations marriott com   To   kprasad iitd gmail com       count   1      so  it matches exactly the specified sub-document  including the field order    For using dot operator  I think it is very clear for every one  Let s see the result of below query    gt  db messages find     headers From    reservations marriott com       count   2   I hope these explanations with the above example will make someone more clarity on find query with sub-documents

User · Answer

The two query mechanism work in different ways  as suggested in the docs at the section Subdocuments   When the field holds an embedded document  i e  subdocument   you can either specify the entire subdocument as the value of a field  or    reach into    the subdocument using dot notation  to specify values for individual fields in the subdocument   Equality matches within subdocuments select documents if the subdocument matches exactly the specified subdocument  including the field order     In the following example  the query matches all documents where the value of the field producer is a subdocument that contains only the field company with the value  ABC123  and the field address with the value  123 Street   in the exact order   db inventory find        producer            company   ABC123           address   123 Street

[mongodb] How to query nested objects?

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