I want to ensure that my users only set one of two fields:
rotations:
- type: weekly
time_restrictions:
# Allow only ONE of the following fields:
weekday_time_of_day: {...}
time_of_day: [...]
I came across the OneOf pattern on Cuetorials, but this does only seem to help when wanting to enforce a schema while writing cue files.
#OneOfTimeRestrictions: {time_of_day: [...string]} | { weekday_time_of_day: {...string} }
rotations: [{
type: *"weekly" | "daily"
restrictions: #oneOf_timerestrictions | {} # won't work, naturally, because nothing is "chosen"
}]
(the the values of the mutually exclusive fields are actually additional, more complex structs, not strings, in case that might matter - but for the sake of a shorter example I've omitted them).
However, I'm trying to vet YAML instead.
The problem is that when defining this:
#OneOfTimeRestrictions:
rotations: [{
type: *"weekly" | "daily"
restrictions: {time_of_day: [...string]} | { weekday_time_of_day: {...string} }
}]
Both fields are acceptable, including when giving them at the same time.
Pointers?
Related
I am learning Firebase after many years of using SQL RDBMSs. This is definitely a challenge.
Say, I have a collection of objects. Each object can belong to any number of categories. Categories have user-editable labels (e.g. user may rename the label after the fact.
SQL RDBMS
So, in RDBMS I would have:
Object table -> { object_id, ... }
Category table -> { category_id, label, ... }
ObjectCategory -> { object_id, category_id }
I see the following options to implement this in Firebase:
1. Objects collection with category label arrays in objects:
/user/objects -> [{ object_id, categories: [ 'category_label1', 'category_label2' ] }, ... ]
Seems yucky. Renaming/deleting a category will mean updating all the objects.
2. Objects referring categories by id
/user/objects -> [{ object_id, categories: [ 'category_id1', 'category_id2' ] }, ... ]
/user/categories -> [{category_id, label, is_deleted: false}, ...]
This seems more reasonable and maintainable. Except sometimes (I think pretty rarely) there will be 2 queries.
3. Collection of object and object categories
/user/objects -> [{object_id1, ...}, {object_id2, ...}]
/user/object_id1/labels -> [{categorylabel1}, {categorylabel2}]
This is largely comparable to option 1 but requires less churn on object documents and makes updates smaller. Renaming/deleting a category becomes a pain.
So, what is the recommended approach?
I have a huge JSON file with lots of stuff I don't care about, and I want to filter it down to only the few keys I care about, preserving the structure. I won't bother if the same key name might occur in different paths and I get both of them. I gleaned something very close from the answers to this question, it taught me how to delete all properties with certain values, like all null values:
del(..|nulls)
or, more powerfully
del(..|select(. == null))
I searched high and low if I could write a predicate over the name of a property when I am looking at a property. I come from XSLT where I could write something like this:
del(..|select(name|test("^(foo|bar)$")))
where name/1 would be the function that returns the property name or array index number where the current value comes from. But it seems that jq lacks the metadata on its values, so you can only write predicates about their value, and perhaps the type of their value (that's still just a feature of the value), but you cannot inspect the name, or path leading up to it?
I tried to use paths and leaf_paths and stuff like that, but I have no clue what that would do and tested it out to see how this path stuff works, but it seems to find child paths inside an object, not the path leading up to the present value.
So how could this be done, delete everything but a set of key values? I might have found a way here:
walk(
if type == "object" then
with_entries(
select( ( .key |test("^(foo|bar|...)$") )
and ( .value != "" )
and ( .value != null ) )
)
else
.
end
)
OK, this seems to work. But I still wonder it would be so much easier if we had a way of querying the current property name, array index, or path leading up to the present item being inspected with the simple recusion ..| form.
In analogy to your approach using .. and del, you could use paths and delpaths to operate on a stream of path arrays, and delete a given path if not all of its elements meet your conditions.
delpaths([paths | select(all(IN("foo", "bar") or type == "number") | not)])
For the condition I used IN("foo", "bar") but (type == "string" and test("^(foo|bar)$")) would work as well. To also retain array elements (which have numeric indices), I added or type == "number".
Unlike in XML, there's no concept of attributes in jq. You'll need to delete from objects.
To delete an element of an object, you need to use del( obj[ key ] ) (or use with_entries). You can get a stream of the keys of an object using keys[]/keys_unsorted[] and filter out the ones you don't want to delete.
Finally, you need to invert the result of test because you want to delete those that don't match.
After fixing these problems, we get the following:
INDEX( "foo", "bar" ) as $keep |
del(
.. | objects |
.[
keys_unsorted[] |
select( $keep[ . ] | not )
]
)
Demo on jqplay
Note that I substituted the regex match with a dictionary lookup. You could use test( "^(?:foo|bar)\\z" ) in lieu of $keep[ . ], but a dictionary lookup should be faster than a regex match. And it should be less error-prone too, considering you misused $ and (...) in lieu of \z and (?:...).
The above visits deleted branches for nothing. We can avoid that by using walk instead of ...
INDEX( "foo", "bar" ) as $keep |
walk(
if type == "object" then
del(
.[
keys_unsorted[] |
select( $keep[ . ] | not )
]
)
else
.
end
)
Demo on jqplay
Since I mentioned one could use with_entries instead of del, I'll demonstrate.
INDEX( "foo", "bar" ) as $keep |
walk(
if type == "object" then
with_entries( select( $keep[ .key ] ) )
else
.
end
)
Demo on jqplay
Here's a solution that uses a specialized variant of walk for efficiency (*). It retains objects all keys of which are removed; only trivial changes are needed if a blacklist or some other criterion (e.g., regexp-based) is given instead. WHITELIST should be a JSON array of the key names to be retained.
jq --argjson whitelist WHITELIST '
def retainKeys($array):
INDEX($array[]; .) as $keys
| def r:
if type == "object"
then with_entries( select($keys[.key]) )
| map_values( r )
elif type == "array" then map( r )
else .
end;
r;
retainKeys($whitelist)
' input.json
(*) Note for example:
the use of INDEX
the recursive function, r, has arity 0
for objects, the top-level deletion occurs first.
Here's a space-efficient, walk-free approach, tailored for the case of a WHITELIST. It uses the so-called "streaming" parser, so the invocation would look like this:
jq -n --stream --argjson whitelist WHITELIST -f program.jq input.json
where WHITELIST is a JSON array of the names of the keys to be deleted, and
where program.jq is a file containing the program:
# Input: an array
# Output: the longest head of the array that includes only numbers or items in the dictionary
def acceptable($dict):
last(label $out
| foreach .[] as $x ([];
if ($x|type == "number") or $dict[$x] then . + [$x]
else ., break $out
end));
INDEX( $whitelist[]; .) as $dict
| fromstream(inputs
| if length==2
then (.[0] | acceptable($dict)) as $p
| if ($p|length) == (.[0]|length) - 1 then .[0] = $p | .[1] = {}
elif ($p|length) < (.[0]|length) then empty
else .
end
else .
end )
Note: The reason this is relatively complicated is that it assumes that you want to retain objects all of whose keys have been removed, as illustrated in the following example. If that is not the case, then the required jq program is much simpler.
Example:
WHITELIST: '["items", "config", "spec", "setting2", "name"]'
input.json:
{
"items": [
{
"name": "issue1",
"spec": {
"config": {
"setting1": "abc",
"setting2": {
"name": "xyz"
}
},
"files": {
"name": "cde",
"path": "/home"
},
"program": {
"name": "apache"
}
}
},
{
"name": {
"etc": 0
}
}
]
}
Output:
{
"items": [
{
"name": "issue1",
"spec": {
"config": {
"setting2": {
"name": "xyz"
}
}
}
},
{
"name": {}
}
]
}
I am going to put my own tentative answer here.
The thing is, the solution I had already in my question, meaning I can select keys during forward navigation, but I cannot find out the path leading up to the present value.
I looked around in the source code of jq to see how come we cannot inquire the path leading up to the present value, so we could ask for the key string or array index of the present value. And indeed it looks like jq does not track the path while it walks through the input structure.
I think this is actually a huge opportunity forfeited that could be so easily kept track during the tree walk.
This is why I continue thinking that XML with XSLT and XPath is a much more robust data representation and tool chain than JSON. In fact, I find JSON harder to read even than XML. The benefit of the JSON being so close to javascript is really only relevant if - as I do in some cases - I read the JSON as a javascript source code assigning it to a variable, and then instrument it by changing the prototype of the anonymous JSON object so that I have methods to go with them. But changing the prototype is said to cause slowness. Though I don't think it does when setting it for otherwise anonymous JSON objects.
There is JsonPath that tries (by way of the name) to be something like what XPath is for XML. But it is a poor substitute and also has no way to navigate up the parent (or then sibling) axes.
So, in summary, while selecting by key in white or black lists is possible in principle, it is quite hard, because a pretty easy to have feature of a JSON navigation language is not specified and not implemented. Other useful features that could be easily achieved in jq is backward navigation to parent or ancestor of the present value. Currently, if you want to navigate back, you need to capture the ancestor you want to get back to as a variable. It is possible, but jq could be massively improved by keeping track of ancestors and paths.
I have the following JSON and am trying to write a JSON Path expression which will return me the isbn number when I have a id of either '123456789' or '987654321'. I tried the following but this did not work. Can anybody tell me what I am doing wrong please. Thanks in advance
JSON Path Expression
$.books[?(#.ids== '123456789' )].isbnNumber
JSON
{
"books": [{
"title": "10",
"isbnNumber": "621197725636",
"ids": [
"123456789",
"987654321"
]
}]
}
The (more traditional) JSONPath implementations that stick close(r) to Goessner's reference specification do not offer handy functions like in which are available in extended implementations like JayWay's JSONPath.
Using Gatling's JSONPath, one thing we could do if the positions of the Ids in question are fixed is accessing their respective indices directly to make the comparison:
$.books[?(#.ids[0] == "123456789" || #.ids[1] == "987654321")].isbnNumber
This will give you the desired result of your example; however, some books only have one of the two indices, or they Id to compare to shows up on a different position it won't work.
I'm a jq newbie, and I try to transform a json (a Swagger spec). I want to add an element to the array value of the "parameter" keys:
{
...
"paths": {
"/great/endpoint1": {
"get": {
"parameters": [] <<--- add a value here
}
}
"/great/endpoint2": {
"post": {
"parameters": [] <<-- and here too here too etc.
....
The following jqplay almost works. It adds values to the right arrays, but it has the nasty side effect of also removing the "x-id" value from the root of the input json. It's probably because of a faulty if-condition. As the paths contain a varying string (the endpoint names), I don't know how to write a wildcard path expression to address those, which is why I have tried using walk instead:
https://jqplay.org/s/az56quLZa3
Since the sample data is incomplete, it's difficult to say exactly what you're looking for but it looks like you should be using parameters in the call to walk:
walk(if type=="object" and has("parameters")
then .parameters += [{"extra": "value"}]
else . end)
If you want to restrict the walk to the top-level paths, you would preface the above with: .paths |=
I am just getting started with eJabberd and am writing a custom module with HTTP access.
I have the request going through, but am now trying to retrieve a custom header and that's where I'm having problems.
I've used the Request record to get the request_headers list and can see that it contains all of the headers I need (although the one I'm after is a binary string on both the key and value for some reason...) as follows:
[
{ 'Content-Length', <<"100">> },
{ <<"X-Custom-Header">>, <<"CustomValue">> },
{ 'Host', <<"127.0.0.1:5280">> },
{ 'Content-Type', <<"application/json">> },
{ 'User-Agent', <<"Fiddler">> }
]
This is also my first foray into functional programming, so from procedural perspective, I would loop through the list and check if the key is the one that I'm looking for and return the value.
To this end, I've created a function as:
find_header(HeaderKey, Headers) ->
lists:foreach(
fun(H) ->
if
H = {HeaderKey, Value} -> H;
true -> false
end
end,
Headers).
With this I get the error:
illegal guard expression
I'm not even sure I'm going about this the right way so am looking for some advice as to how to handle this sort of scenario in Erlang (and possibly in functional languages in general).
Thanks in advance for any help and advice!
PhilHalf
The List that you have mentioned is called a "Property list", which is an ordinary list containing entries in the form of either tuples, whose first elements are keys used for lookup and insertion or atoms, which work as shorthand for tuples {Atom, true}.
To get a value of key, you may do the following:
proplists:get_value(Key,List).
for Example to get the Content Length:
7> List=[{'Content-Length',<<"100">>},
{<<"X-Custom-Header">>,<<"CustomValue">>},
{'Host',<<"127.0.0.1:5280">>},
{'Content-Type',<<"application/json">>},
{'User-Agent',<<"Fiddler">>}].
7> proplists:get_value('Content-Type',List).
<<"application/json">>
You can use the function lists:keyfind/3:
> {_, Value} = lists:keyfind('Content-Length', 1, Headers).
{'Content-Length',<<"100">>}
> Value.
<<"100">>
The 1 in the second argument tells the function what tuple element to compare. If, for example, you wanted to know what key corresponds to a value you already know, you'd use 2 instead:
> {Key, _} = lists:keyfind(<<"100">>, 2, Headers).
{'Content-Length',<<"100">>}
> Key.
'Content-Length'
As for how to implement this in Erlang, you'd write a recursive function.
Imagine that you're looking at the first element of the list, trying to figure out if this is the entry you're looking for. There are three possibilities:
The list is empty, so there is nothing to compare.
The first entry matches. Return it and ignore the rest of the list.
The first entry doesn't match. Therefore, the result of looking for this key in this list is the same as the result of looking for it in the remaining elements: we recurse.
find_header(_HeaderKey, []) ->
not_found;
find_header(HeaderKey, [{HeaderKey, Value} | _Rest]) ->
{ok, Value};
find_header(HeaderKey, [{_Key, _Value} | Rest]) ->
find_header(HeaderKey, Rest).
Hope this helps.