In Pymongo application, while iterating through every document of the collection, how to access a specific field value of the JSON structure?
{
"_id": {
"$oid": "5e1c2b0bacbdaehujjjbdsh"
},
"a": {
"data_type": "abc",
"data_format": "xyz",
"data_version": "1",
},
"b": "123",
"c": "345"
}
Based on the following code snippet, how do I access the value associated with the key 'data_format' which is nested within the key 'a' ---
for document in col.find():
data_format_val = document['a']['data_format'] # not working
Relatively new to Mongodb query commands.
It's possible that some of the documents of the collection may not have the key 'a'.
Try using $exists to make sure the field is present like this: Syntax: { field: { $exists: } }
Related
I have got a collection of documents and each documents contains a nested array of objects.
{
"id": "309324739",
"debters": [
{
"user": {
"name": "John Doe",
"internal": true
},
"debt": 1463,
},
{
"user": {
"name": "Alex Tree",
"internal": false
},
"debt": 53443,
},
}
What I'm trying to do is to return find the document by id and then find inside the debters list that has a false flag?
I tried the following query...
Debters findByIdAndDebters_User_InternalIsFalse(#Param("id") String id,);
But I'm getting an error saying that it can find "internal" property. What am I doing wrong and how can I loop through array using this magic mongo repository query?
you need to write a native query for that which is similar to
#Query("{'debters.user.internal':false,'_id':''}")
Debters findByIdAndDebtersUserInternalIsFalse(#Param("id") String id,);
Lets say I have a collection whose objects have a structure like this:
{
"a": [
{"name": "foo", "meh": "whatever"},
{"name": "bar", "meh": "hem"}
],
"other_stuff": { }
}
It's possible for an object in this collection to not have the "a" field. I'd like to enforce a constraint on the database such that, if an object has the "a" field, that none of the "name" fields in objects contained in that "a" field are duplicates across the entire collection.
So for example, the following object would be flagged as a constraint violation if the above object were already in the collection:
{
"a": [
{"name": "bar", "meh": "meh meh"}
],
"other_stuff": { }
}
Furthermore, the following object would be flagged as a constraint violation regardless of other documents already in the collection:
{
"a": [
{"name": "boo", "meh": "blub"},
{"name": "boo", "meh": "glub"}
],
"other_stuff": { }
}
Is it possible to specify a partial unique index for MongoDB? If it's different between Mongo 3.2, 3.4, 3.6 and 4.0 it would be nice to know that too - I don't care about earlier than 3.2.
I was thinking it might be something like this to prevent duplication across documents (because in Javscript [] > '' === false and undefined > '' === false and ['anything'] > '' === true for the passive reader):
db.MyCollection.createIndex(
{ "a.name": 1 },
{
"unique": true,
"partialFilterExpression": {
"a": { "$gt": '' }
}
}
)
... and I think the only way to prevent duplicate values within a document is to enforce in application logic the use of the $addToSet operator when operating on the "a" field.
I'd be happy to be corrected or corroborated on either count.
My recent project encountered the same problem as this one: the question
db.test.update(
{name:"abc123", "config.a":1 },
{$addToSet:{ config:{a:1,b:2} } },
true
)
Will produce such error:
Cannot apply $addToSet to a non-array field
But after changed to:
db.test.update(
{name:"abc123", "config.a":{$in:[1]} },
{$addToSet:{ config:{a:1,b:2} } },
true
)
It works fine.
Also referenced this link: Answer
Can Any one explain what's going on? "config.a":1 will turn config to be an object? Where "config.a":{$in:[1]} won't?
What you are trying to do here is add a new item to an array only where the item does not exist and also create a new document where it does not exist. You choose $addToSet because you want the items to be unique, but in fact you really want them to be unique by "a" only.
So $addToset will not do that, and you rather need to "test" the element being present. But the real problem here is that it is not possible to both do that and "upsert" at the same time. The logic cannot work as a new document will be created whenever the array element was not found, rather than append to the array element like you want.
The current operation errors by design as $addToSet cannot be used to "create" an array, but only to "add" members to an existing array. But as stated already, you have other problems with achieving the logic.
What you need here is a sequence of update operations that each "try" to perform their expected action. This can only be done with multiple statements:
// attempt "upsert" where document does not exist
// do not alter the document if this is an update
db.test.update(
{ "name": "abc" },
{ "$setOnInsert": { "config": [{ "a": 1, "b": 2 }] }},
{ "upsert": true }
)
// $push the element where "a": 1 does not exist
db.test.update(
{ "name": "abc", "config.a": { "$ne": 1 } },
{ "$push": { "config": { "a": 1, "b": 2 } }}
)
// $set the element where "a": 1 does exist
db.test.update(
{ "name": "abc", "config.a": 1 },
{ "$set": { "config.$.b": 2 } }
)
On a first iteration the first statement will "upsert" the document and create the array with items. The second statement will not match the document because the "a" element has the value that was specified. The third statement will match the document but it will not alter it in a write operation because the values have not changed.
If you now change the input to "b": 3 you get different responses but the desired result:
db.test.update(
{ "name": "abc" },
{ "$setOnInsert": { "config": [{ "a": 1, "b": 3 }] }},
{ "upsert": true }
)
db.test.update(
{ "name": "abc", "config.a": { "$ne": 1 } },
{ "$push": { "config": { "a": 1, "b": 3 } }}
)
db.test.update(
{ "name": "abc", "config.a": 1 },
{ "$set": { "config.$.b": 3 } }
)
So now the first statement matches a document with "name": "abc" but does not do anything since the only valid operations are on "insert". The second statement does not match because "a" matches the condition. The third statment matches the value of "a" and changes "b" in the matched element to the desired value.
Subsequently changing "a" to another value that does not exist in the array allows both 1 and 3 to do nothing but the second statement adds another member to the array keeping the content unique by their "a" keys.
Also submitting a statement with no changes from existing data will of course result in a response that says nothing is changed on all accounts.
That's how you do your operations. You can do this with "ordered" Bulk operations so that there is only a single request and response from the server with the valid response to modified or created.
As explained in this issue on the MongoDB JIRA (https://jira.mongodb.org/browse/SERVER-3946), this can be solved in a single query:
The following update fails because we use $addToSet on a field which we have also included in the first argument (the field which accepts the fields and values to query for). As far as I understand it, you can't use upsert: true in this scenario where we $addToSet to the same field we query with.
db.foo.update({x : "a"}, {$addToSet: {x: "b"}} , {upsert: true}); // FAILS
The solution is to use $elemMatch: {$eq: field: value}
db.foo.update({x: {$elemMatch: {$eq: "a"}}}, {$addToSet: {x: "b"}}, {upsert: true});
Is it possible to query mongodb to return array of matching document id values, without the related keys?
Please consider following 'parent' data structur:
{
"_id": ObjectId("52448e4697fb2b775cb5c3a7"),
"name": "Peter",
"children": [
{
"name": "joe"
}
]
},
{
"_id": ObjectId("52448e4697fb2b775cb5c3b6"),
"name": "Marry",
"children": [
{
"name": "joe"
}
]
}
I would to query for an array of parent _ids whose children have the name "joe"
For provided sample data, I would like the following output returned from mongo:
[ObjectId("52448e4697fb2b775cb5c3a7"), ObjectId("52448e4697fb2b775cb5c3b6")]
I know that I can query for an output like this, which also contains the keys
[{"_id": ObjectId("52448e4697fb2b775cb5c3a7")}, {"_id": ObjectId("52448e4697fb2b775cb5c3b6")}]
However I need to push above array to another document with an update operation like this:
db.statistic.update({"date": today}, {$push: {"children": [ObjectId("52448e4697fb2b775cb5c3a7"), ObjectId("52448e4697fb2b775cb5c3b6")]}}, true, false)
I would like to avoid sorting out the document structure, in case it is possible to just return an array containing the appropriate values using mongo
It should be possible by
db.coll.distinct("_id", {"children.name": "joe"})
To clarify: I have a document with a subdoc. I create a new document with the same data of the other one and it gets a new id. However, when I copy the subdoc array they do not get a new id.
Are subdocs id local to the parent doc? I.e. would the following be a problem?
[
{
"__v": 1,
"_id": "5214af03a9f53efa61000004",
"name": "Foo",
"subdocs": [
{
"thing": "value",
"_id": "5214af03a9f53efa61000006"
}
]
},
{
"__v": 0,
"name": "Foo",
"_id": "5214af03a9f53efa61000014",
"subdocs": [
{
"thing": "value",
"_id": "5214af03a9f53efa61000006"
}
]
}
]
There is a unique index on the _id field of documents stored directly in a collection, but not for embedded documents, nor is there any requirement that embedded documents have an _id field at all. The two documents you have provided are both valid to be stored in MongoDB in the same database (I'm interpreting your example as an array of two documents that are both stored directly in a collection together).