I have a Companies table in DynamoDB that looks like this:
company: {
id: "11",
name: "test",
jobs: [
{
"name": "painter",
"id": 3
},
{
"name": "gardner"
"id": 2
}
]
}
And I want to make a scan query that get all the companies with the "painter" job inside their jobs array
I am using python and boto3
I tried something like this but it didn't work
jobs = ["painter"]
response = self.table.scan(
FilterExpression=Attr('jobs.name').is_in(jobs)
)
Please help.
Thanks.
It looks like this may not be doable in general, however it's possible that the method applied in that link may still be useful. If you know the maximum length of the jobs array over all of your data, you could create an expression for each index chained with ORs. Notably I could not find documentation for handling map and list scan expressions, so I can't really say whether you'd also need to check that you're not going out of bounds.
Related
in my database, there are two companies with same name.
[
{
"name": "samsung",
"store_code": "34d"
},
{
"name": "lg",
"store_code": "333"
},
{
"name": "lg",
"store_code": "3511"
}
]
like this..
my question is, I juse made my python function to get store information by name.
that looks like this..
async def fetch_store_by_name(store_name):
document = collection.find_one({"name":store_name})
return document
and I can only get the first lg company's information.
how can I get both informations of lg company from my mongodb?
Use find instead of find_one .
https://www.w3schools.com/python/python_mongodb_find.asp
I assumed you're using pymongo, just change find_one to find method. Like this:
async def fetch_store_by_name(store_name):
document = collection.find({"name":store_name})
return document
Here some documentation : https://pymongo.readthedocs.io/en/stable/tutorial.html#querying-for-more-than-one-document
You can use collection.find({"name":store_name})
Reference:
https://www.w3schools.com/python/python_mongodb_find.asp
Using variables such as name, address, zip code to identify a document is not a good approach as there may be the same names, names with different cases, spaces ex: LG, lg.
You can use the default mongo _id as a unique property to find the doc. Still you want to get the document then use collection.find({"name":store_name}) it will returns multiple documents ab array. If you want to retrieve only one doc then use collection.findOne({"name":store_name})
I have a json called thefile.json which looks like this:
{
"domain": "Something",
"domain": "Thingie",
"name": "Another",
"description": "Thing"
}
I am trying to write a python script which would made a set of the values in domain. In this example it would return
{'Something', 'Thingie'}
Here is what I tried:
import json
with open("thefile.json") as my_file:
data = json.load(my_file)
ids = set(item["domain"] for item in data.values())
print(ids)
I get the error message
unique_ids.add(item["domain"])
TypeError: string indices must be integers
Having looked up answers on stack exchange, I'm stumped. Why can't I have a string as an index, seeing as I am using a json whose data type is a dictionary (I think!)? How do I get it so that I can get the values for "domain"?
So, to start, you can read more about JSON formats here: https://www.w3schools.com/python/python_json.asp
Second, dictionaries must have unique keys. Therefore, having two keys named domain is incorrect. You can read more about python dictionaries here: https://www.w3schools.com/python/python_dictionaries.asp
Now, I recommend the following two designs that should do what you need:
Multiple Names, Multiple Domains: In this design, you can access websites and check the domain of each of its values like ids = set(item["domain"] for item in data["websites"])
{
"websites": [
{
"domain": "Something.com",
"name": "Something",
"description": "A thing!"
},
{
"domain": "Thingie.com",
"name": "Thingie",
"description": "A thingie!"
},
]
}
One Name, Multiple Domains: In this design, each website has multiple domains that can be accessed using JVM_Domains = set(data["domains"])
{
"domains": ["Something.com","Thingie.com","Stuff.com"]
"name": "Me Domains",
"description": "A list of domains belonging to Me"
}
I hope this helps. Let me know if I missed any details.
You have a problem in your JSON, duplicate keys. I am not sure if it is forbiden, but I am sure it is bad formatted.
Besides that, of course it is gonna bring you lot of problems.
A dictionary can not have duplicate keys, what would be the return of a duplicate key?.
So, fix your JSON, something like this,
{
"domain": ["Something", "Thingie"],
"name": "Another",
"description": "Thing"
}
Guess what, good format almost solve your problem (you can have duplicates in the list) :)
I'm trying to get a list of instance IDs that I get from the describe_instances call using boto3 api in my python script. For those of you who aren't aware of aws, I can post a detailed code after removing the specifics if you need it. I'm trying to access a item from a structure like this
u'Reservations':[
{
u'Instances':[
{
u'InstanceId':'i-0000ffffdd'
},
{ }, ### each of these dict contain a id like above
{ },
{ },
{ }
]
},
{
u'Instances':[
{ },
{ },
{ },
{ },
{ }
]
},
{
u'Instances':[
{ }
]
}
]
I'm currently accessing it like
instanceLdict = []
instanceList = []
instances = []
for r in reservations:
instanceList.append(r['Instances'])
for ilist in instanceList:
for i in ilist:
instanceLdict.append(i)
for i in instanceLdict:
instances.append(i['InstanceId']) ####i need them in a list
print instances
fyi: my reservations variable contains the whole list of u'Reservations':
I feel this is inefficient and since I'm a python newbie I really think there must be some better way to do this rather than the multiple for and if. Is there a better way to do this? Kindly point to the structure/method etc., that might be useful in my scenario
Your solution is not actually that inefficient, except you don't really have to create all those top level lists just to save the instance ids in the end. What you could do is a nested loop and keep only what you need:
instances = list()
for r in reservations:
for ilist in r['Instances']:
for i in ilist:
instances.append(i['InstanceId']) # That's what you looping for
Yes, there are ways to do this with shorter code, but explicit is better than implicit and stick to what you can read best. Python is quite good with iterations and remember maintainability first, performance second. Also, this part is hardly the bottleneck of what you doing after all those API calls, DB lookups etc.
But if you really insist to do fancy one-liner, go have a look at itertools helpers, chain.from_iterable() is what you need:
from itertools import chain
instances = [i['InstanceId'] for i in chain.from_iterable(r['Instances'] for r in reservations)]
I am trying to update a value in the nested array but can't get it to work.
My object is like this
{
"_id": {
"$oid": "1"
},
"array1": [
{
"_id": "12",
"array2": [
{
"_id": "123",
"answeredBy": [], // need to push "success"
},
{
"_id": "124",
"answeredBy": [],
}
],
}
]
}
I need to push a value to "answeredBy" array.
In the below example, I tried pushing "success" string to the "answeredBy" array of the "123 _id" object but it does not work.
callback = function(err,value){
if(err){
res.send(err);
}else{
res.send(value);
}
};
conditions = {
"_id": 1,
"array1._id": 12,
"array2._id": 123
};
updates = {
$push: {
"array2.$.answeredBy": "success"
}
};
options = {
upsert: true
};
Model.update(conditions, updates, options, callback);
I found this link, but its answer only says I should use object like structure instead of array's. This cannot be applied in my situation. I really need my object to be nested in arrays
It would be great if you can help me out here. I've been spending hours to figure this out.
Thank you in advance!
General Scope and Explanation
There are a few things wrong with what you are doing here. Firstly your query conditions. You are referring to several _id values where you should not need to, and at least one of which is not on the top level.
In order to get into a "nested" value and also presuming that _id value is unique and would not appear in any other document, you query form should be like this:
Model.update(
{ "array1.array2._id": "123" },
{ "$push": { "array1.0.array2.$.answeredBy": "success" } },
function(err,numAffected) {
// something with the result in here
}
);
Now that would actually work, but really it is only a fluke that it does as there are very good reasons why it should not work for you.
The important reading is in the official documentation for the positional $ operator under the subject of "Nested Arrays". What this says is:
The positional $ operator cannot be used for queries which traverse more than one array, such as queries that traverse arrays nested within other arrays, because the replacement for the $ placeholder is a single value
Specifically what that means is the element that will be matched and returned in the positional placeholder is the value of the index from the first matching array. This means in your case the matching index on the "top" level array.
So if you look at the query notation as shown, we have "hardcoded" the first ( or 0 index ) position in the top level array, and it just so happens that the matching element within "array2" is also the zero index entry.
To demonstrate this you can change the matching _id value to "124" and the result will $push an new entry onto the element with _id "123" as they are both in the zero index entry of "array1" and that is the value returned to the placeholder.
So that is the general problem with nesting arrays. You could remove one of the levels and you would still be able to $push to the correct element in your "top" array, but there would still be multiple levels.
Try to avoid nesting arrays as you will run into update problems as is shown.
The general case is to "flatten" the things you "think" are "levels" and actually make theses "attributes" on the final detail items. For example, the "flattened" form of the structure in the question should be something like:
{
"answers": [
{ "by": "success", "type2": "123", "type1": "12" }
]
}
Or even when accepting the inner array is $push only, and never updated:
{
"array": [
{ "type1": "12", "type2": "123", "answeredBy": ["success"] },
{ "type1": "12", "type2": "124", "answeredBy": [] }
]
}
Which both lend themselves to atomic updates within the scope of the positional $ operator
MongoDB 3.6 and Above
From MongoDB 3.6 there are new features available to work with nested arrays. This uses the positional filtered $[<identifier>] syntax in order to match the specific elements and apply different conditions through arrayFilters in the update statement:
Model.update(
{
"_id": 1,
"array1": {
"$elemMatch": {
"_id": "12","array2._id": "123"
}
}
},
{
"$push": { "array1.$[outer].array2.$[inner].answeredBy": "success" }
},
{
"arrayFilters": [{ "outer._id": "12" },{ "inner._id": "123" }]
}
)
The "arrayFilters" as passed to the options for .update() or even
.updateOne(), .updateMany(), .findOneAndUpdate() or .bulkWrite() method specifies the conditions to match on the identifier given in the update statement. Any elements that match the condition given will be updated.
Because the structure is "nested", we actually use "multiple filters" as is specified with an "array" of filter definitions as shown. The marked "identifier" is used in matching against the positional filtered $[<identifier>] syntax actually used in the update block of the statement. In this case inner and outer are the identifiers used for each condition as specified with the nested chain.
This new expansion makes the update of nested array content possible, but it does not really help with the practicality of "querying" such data, so the same caveats apply as explained earlier.
You typically really "mean" to express as "attributes", even if your brain initially thinks "nesting", it's just usually a reaction to how you believe the "previous relational parts" come together. In reality you really need more denormalization.
Also see How to Update Multiple Array Elements in mongodb, since these new update operators actually match and update "multiple array elements" rather than just the first, which has been the previous action of positional updates.
NOTE Somewhat ironically, since this is specified in the "options" argument for .update() and like methods, the syntax is generally compatible with all recent release driver versions.
However this is not true of the mongo shell, since the way the method is implemented there ( "ironically for backward compatibility" ) the arrayFilters argument is not recognized and removed by an internal method that parses the options in order to deliver "backward compatibility" with prior MongoDB server versions and a "legacy" .update() API call syntax.
So if you want to use the command in the mongo shell or other "shell based" products ( notably Robo 3T ) you need a latest version from either the development branch or production release as of 3.6 or greater.
See also positional all $[] which also updates "multiple array elements" but without applying to specified conditions and applies to all elements in the array where that is the desired action.
I know this is a very old question, but I just struggled with this problem myself, and found, what I believe to be, a better answer.
A way to solve this problem is to use Sub-Documents. This is done by nesting schemas within your schemas
MainSchema = new mongoose.Schema({
array1: [Array1Schema]
})
Array1Schema = new mongoose.Schema({
array2: [Array2Schema]
})
Array2Schema = new mongoose.Schema({
answeredBy": [...]
})
This way the object will look like the one you show, but now each array are filled with sub-documents. This makes it possible to dot your way into the sub-document you want. Instead of using a .update you then use a .find or .findOne to get the document you want to update.
Main.findOne((
{
_id: 1
}
)
.exec(
function(err, result){
result.array1.id(12).array2.id(123).answeredBy.push('success')
result.save(function(err){
console.log(result)
});
}
)
Haven't used the .push() function this way myself, so the syntax might not be right, but I have used both .set() and .remove(), and both works perfectly fine.
In my project I have to use the Eventregistry.org events API to search for specific articles with specific keywords.
The problem is that if I add more than one keyword, it seems to perform an "AND" sort of search instead of an "OR". (searched for ipad alone ~8k results, searched for surface alone ~40k results, searched for ipad surface together got 9 results)
I am using cakephp 3, but I think the language is not the problem, I think is the final url. I went went through the Python project and find some Query.AND(params) and Query.OR(params) so I asume that this can be done?, but I don't know Python.
This is my url:
http://eventregistry.org/json/article?ignoreKeywords=&keywords=surface%20ipad&lang=eng&action=getArticles&articlesSortBy=date&resultType=articles&articlesCount=20
Here you can test the API
This is the Python repo on github
Well, their documentation is not overly informative, to say the least.
Looks like they're using some kind of query language, you could probably figure out what things look like by debugging the request generated by the Python script, but if you're not familiar with Python, try using their web interface instead, apparently it supports boolean conditions (OR, AND, NOT, the latter being expressed as -), which are being composed into a JSON structure:
http://blog.eventregistry.org/.../phrase-search-boolean-keyword-queries-web-interface
http://blog.eventregistry.org/2017/05/15/number-changes-api-users
Check your browsers network console to inspect the generated URLs, they'll contain a query key that holds a JSON string like this:
{"$query":{"$and":[{"$or":[{"keyword":{"$and":["ipad"]}},{"keyword":{"$and":["surface"]}}]}]}}
{
"$query": {
"$and": [
{
"$or": [
{
"keyword": {
"$and": [
"ipad"
]
}
},
{
"keyword": {
"$and": [
"surface"
]
}
}
]
}
]
}
}
That looks a little different to what the blog post shows, but it seems that the more compact variant shown there works too:
{"$query":{"keyword":{"$or":["ipad","surface"]}}}
{
"$query": {
"keyword": {
"$or": [
"ipad",
"surface"
]
}
}
}
So the final URL could look like this:
http://eventregistry.org/json/article?action=getArticles&articlesCount=20&articlesSortBy=date&resultType=articles&query={"$query":{"keyword":{"$or":["ipad","surface"]}}}
http://eventregistry.org/json/article
?action=getArticles
&articlesCount=20
&articlesSortBy=date
&resultType=articles
&query={"$query":{"keyword":{"$or":["ipad","surface"]}}}