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Consequences of using $unwind on nested arrays?


Consequences of using $unwind on nested arrays?

By : user2949585
Date : November 17 2020, 01:00 AM
I wish did fix the issue. It is always a good idea to be cognizant of memory resources when $unwinding because of the replication of data that occurs.
Using $match to narrow down the results to the specific documents you are looking for is of course one way to reduce the amount of memory necessary to hold the returned data.
code :
{
  someInfo: "blah blah blah",
  answers: [
    {
      email: "test@test.com",
      values: [
        {value: 1, label: "test1"},
        {value: 2, label: "test2"}    
      ]
    },
    {
      email: "someone@somewhere.com",
      values: [
        {value: 6, label: "test1"},
        {value: 1, label: "test2"}    
      ]
    }
  ]
}
db.collection.aggregate([{ $match: { <element>: <value> }}, { $project: { _id: 0, answers: 1}}])
db.collection.aggregate([
   { $match: { <element>: <value> }},
   { $project: { _id: 0, answers: 1}},
   { $unwind: "$answers"},
   { $unwind: "$answers.tags"},
   { $project: { e: "$answers.email", v: "$answers.values"}}
])
{ e: "test@test.com", v: { value: 1, label: "test1" } }
{ e: "test@test.com", v: { value: 2, label: "test2" } }
{ e: "someone@somewhere.com", v: { value: 6, label: "test1" } }
{ e: "someone@somewhere.com", v: { value: 1, label: "test2" } }


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Neo4j - Nested Collection By Using UNWIND and MERGE With Error: Property values can only be of primitive types or arrays

Neo4j - Nested Collection By Using UNWIND and MERGE With Error: Property values can only be of primitive types or arrays


By : SivaKiran SK
Date : March 29 2020, 07:55 AM
Hope this helps Property values can not be nested. This means, for example, that an array property can only contain primitive values (of the same type).
You may want to consider having separate Address nodes related to each Person.
MongoDB update objects nested in arrays nested in other arrays without using the array index (nested updating)

MongoDB update objects nested in arrays nested in other arrays without using the array index (nested updating)


By : kazim raseed
Date : March 29 2020, 07:55 AM
like below fixes the issue Sadly no, the positional operator can only hold a single value. I don't think you can perform this update in a single shot with your current data structure.
You could perform one lookup to get the first array index, then a second with the positional operator, but at that point you could just traverse the array and resave the document.
Unwind in mongodb aggregate with multiple nested, but possibly empty, arrays

Unwind in mongodb aggregate with multiple nested, but possibly empty, arrays


By : Adam
Date : March 29 2020, 07:55 AM
wish help you to fix your issue You can do this in MongoDB 3.2+ by including the preserveNullAndEmptyArrays: true option in the relevant $unwind stages:
code :
aggregate( [
  { $match: { _id: <id>} },
  { $unwind: { path: '$arrayOne', preserveNullAndEmptyArrays: true } },
  { $unwind: '$arrayOne.listings' },
  { $unwind: { path: '$arrayTwo', preserveNullAndEmptyArrays: true } },
  { $unwind: '$arrayTwo.listings' },
  { $group : { _id : '$_id', setOne: { $addToSet: '$arrayOne.listings'}, setTwo: {$addToSet: '$arrayTwo.listings'} } },
  { $project: {unique_appearances: {$setUnion: ['$setOne', '$setTwo']}}}
] );
Initializing arrays, potentially unforseen consequences?

Initializing arrays, potentially unforseen consequences?


By : JBDevionn
Date : March 29 2020, 07:55 AM
it should still fix some issue It's because it's part of the C++ spec1, §11.6.2, which discusses the behavior of initializing character (or wide character) arrays using string literals:
How can I achieve mongo "unwind" in postgres JSONB? (Flatten nested arrays)

How can I achieve mongo "unwind" in postgres JSONB? (Flatten nested arrays)


By : G. Putnam
Date : March 29 2020, 07:55 AM
it should still fix some issue I recently looked into migrating our product database from mongo to postgres. Coming from mongoDb, I am used of "unwinding" objects and arrays. , The function:
code :
create or replace function jsonb_unwind(target jsonb, path text[])
returns jsonb language plpgsql as $$
begin
    if jsonb_typeof(target #> path) = 'array' then
        return jsonb_set(target, path, target #> path -> 0);
    else
        return target;
    end if;
end $$;
select 
    jsonb_unwind(
        jsonb_unwind(json_data, '{colorVariants}'), 
        '{colorVariants, sizeVariants}')
from my_table;
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