get a datetime from mongo and push it to the array - mongodb

Question

I have documents with the following props:
{
'published_date': '2020/03/10 07:20:09',
'relationships': [
{'rel_name': 'HAS_REL'},
{'rel_name': 'HAS_NO_REL'},
]
}
I want to add in each field of relationships that has as rel_name the value of HAS_REL the value of the published date as the property dict. The document will become as follows:
{
'published_date': '2020/03/10 07:20:09',
'relationships': [
{ 'rel_name': 'HAS_REL'
'date': 2020,03,10,07,20,09
},
{'rel_name': 'HAS_NO_REL'},
]
}
So far my query looks something like this:
TEST_COLLECTION.update_one(
{'_id': ObjectId(document_id)},
{'$set': {'relationships.$[elem].date': {'$dateFromString': '$published_date'}}},
False,
False,
None,
[{'elem.rel_name': 'HAS_RELATIONSHIP'}],
)
But I'm getting the error:
WriteError: The dollar ($) prefixed field '$dateFromString' in 'parsed.relationships.1.date.$dateFromString' is not valid for storage.
any ideas?
UPDATE
With the initial answer, I've updated the query such as follows:
TEST_COLLECTION.update_one(
{'_id': ObjectId(document_id)},
[
{'$set': {
'relationships': {
'$let': {
'vars': {
'date': { '$dateFromString': { 'dateString': '$published_date', format: "%Y/%m/%d %H:%M:%S" } }
},
'in': {
'$map': {
'input': "$relationships",
'in': {
'$cond': {
'if': { '$eq': ["$$this.rel_name", "HAS_REL"] },
'then': { '$mergeObjects': ["$$this", { 'date': "$$date" }] },
'else': "$$this"
}
}
}
}
}
}
}
}
]
)
However, it seems I'me not getting a correct document:
InvalidDocument: documents must have only string keys, key was
built-in function format

Answer 1

Have a look at $dateFromString
You have to specify format field, unless you use default format "%Y-%m-%dT%H:%M:%S.%LZ". Storing date/time values as string is usually a design flaw.
So, it must be
{'$dateFromString': { dateString: '$published_date', format: "%Y/%m/%d %H:%M:%S" } }
Note, the time is considered at UTC time. Set field timezone to specify the time zone if required.
Be aware, $dateFromString() is an aggregation function, so you must use
TEST_COLLECTION.update_one(
{ '_id': ObjectId(document_id) },
[
{
$set: {
relationships: {
$map: {
input: "$relationships",
in: {
$cond: {
if: { $eq: ["$$this.rel_name", "HAS_REL"] },
then: {
$mergeObjects: [
"$$this",
{
date: {
$dateFromString: {
dateString: '$published_date',
format: "%Y/%m/%d %H:%M:%S"
}
}
}
]
},
else: "$$this"
}
}
}
}
}
}
]
)
or another style:
TEST_COLLECTION.update_one(
{ '_id': ObjectId(document_id) },
[
{
$set: {
relationships: {
$let: {
vars: {
date: { $dateFromString: { dateString: '$published_date', format: "%Y/%m/%d %H:%M:%S" } }
},
in: {
$map: {
input: "$relationships",
in: {
$cond: {
if: { $eq: ["$$this.rel_name", "HAS_REL"] },
then: { $mergeObjects: ["$$this", { date: "$$date" }] },
else: "$$this"
}
}
}
}
}
}
}
}
]
)