I'm using Postgrex in Elixir, and when it returns query results, it returns them in the following struct format:
%{columns: ["id", "email", "name"], command: :select, num_rows: 2, rows: [{1, "me#me.com", "Bobbly Long"}, {6, "email#tts.me", "Woll Smoth"}]}
It should be noted I am using Postgrex directly WITHOUT Ecto.
The columns (table headers) are returned as a collection, but the results (rows) are returned as a list of tuples. (which seems odd, as they could get very large).
I'm trying to find the best way to programmatically create JSON objects for each result in which the JSON key is the column title and the JSON value the corresponding value from the tuple.
I've tried creating maps from both, merging and then serialising to JSON objects but it seems there should be an easier/better way of doing this.
Has anyone dealt with this before? What is the best way of creating a JSON object from a separate collection and tuple?
Something like this should work:
result = Postgrex.query!(...)
Enum.map(result.rows, fn row ->
Enum.zip(result.columns, Tuple.to_list(row))
|> Enum.into(%{})
|> JSON.encode
end)
This will result in a list of json objects where each row in the resultset is a json object.
Related
Many similar questions, but unfortunately non helped me solve my problem. I tried to && and #> and similar, but no success.
I have a postgres DB with a table, that has a "value" column typed "json". All rows have the same basic structure, a simple JSON object, with the att "value" holding an array of strings:
{
value: ['one', 'two', 'three']
}
I need to make a query accepting an array of strings and returns all the rows, in which the value array and the passed array of strings have at least one common element.
Following the upper example, if I send ['one', 'four'], it should return the row with value: ['one', 'two', 'three'], since there is an intersection - 'one'.
If I send the array ['four', 'five', 'six'], it will not return this row.
You can use the ?| operator for that. But as you are using json and not the recommended jsonb type, you need to cast your column:
select *
from the_table
where (value::jsonb -> 'value') ?| array['one', 'four']
Most examples deal with the book store example from Stefan Gössner, however I'm struggling to define the correct JsonPath expression for a simple object (no array):
{ "Id": 1, "Name": "Test" }
To check if this json contains Id = 1.
I tried the following expression: $..?[(#.Id == 1]), but this does find any matches using Json.NET?
Also tried Manatee.Json for parsing, and there it seems the jsonpath expression could be like $[?($.Id == 1)] ?
The path that you posted is not valid. I think you meant $..[?(#.Id == 1)] (some characters were out of order). My answer assumes this.
The JSON Path that you're using indicates that the item you're looking for should be in an array.
$ start
.. recursive search (1)
[ array item specification
?( item-based query
#.Id == 1 where the item is an object with an "Id" with value == 1 at the root
) end item-based query
] end array item specification
(1) the conditions following this could match a value no matter how deep in the hierarchy it exists
You want to just navigate the object directly. Using $.Id will return 1, which you can validate in your application.
All of that said...
It sounds to me like you want to validate that the Id property is 1 rather than to search an array for an object where the Id property is 1. To do this, you want JSON Schema, not JSON Path.
JSON Path is a query language for searching for values which meet certain conditions (e.g. an object where Id == 1.
JSON Schema is for validating that the JSON meet certain requirements (your data's in the right shape). A JSON Schema to validate that your object has a value of 1 could be something like
{
"properties": {
"Id": {"const":1}
}
}
Granted this isn't very useful because it'll only validate that the Id property is 1, which ideally should only be true for one object.
I have spatial query for postgresql (and postgis). I use raw() function. So I have something like this:
observations = Square.objects.raw('SELECT validation_birds_square.id AS id,
validation_birds_square.identification,
Count(validation_birds_checklist.position) AS total
FROM validation_birds_square ...the rest of sql query...')
I use Square model which I defined in my models.py. Then I want serialize observations, so I make this:
return HttpResponse(serializers.serialize("json", observations), content_type='application/json')
But here is the problem. It serialize only properties of Square model, not total from sql query.
When I iterate over observations I can get that value:
for observation in observations:
print(observation.total)
Is there any better way how to put total to serialized JSON than iterate over observations and serialize it manually to JSON?
You don't have a proper queryset, so there isn't much point in using the built-in serializers. Just create a list of dicts, and use JsonResponse to return it as JSON.
data = [{'id': o.id, 'identification': o.identification, 'total': o.total} for o in observations]
return JsonResponse(data)
The default output of JsonConvert.SerializeObject(ds2, Formatting.Indented) is an array of objects. I'd like to get an array of arrays with just the row data and not reapeating of the column name in each row.
I'd like to be able to present my recordset to DataTables as an array of columns and an array of row data items. Getting the column names into a variable is pretty easy and fast, but I'm wondering what's the fastest way to get the row data into an array.
I'm not interested in compressing the data in transit as described in another answer. The data needs to be processed on the client side in a jQuery DataTable. The more rows returned the slower the JavaScript gets.
To be clear, I want the JSON Serializer to return data in the following format:
aoColumns: [
"Name",
"Age",
"Location"
],
aaData: [
["Bob", 32, "Group1"],
["Sara", 43, "Group1"],
["Gary", 41, "Group2"]
]
aaData could be any name as DataTables can be told where to find the data and the column names.
I have a list of JSON objects (received from a nosql db) and want to remove or rename some keys. And then I want to return data as a list of JSON objects once again.
This Stackoverflow post provides a good sense of how to use mochijson2. And I'm thinking I could use a list comprehension to go through the list of JSON objects.
The part I am stuck with is how to remove the key for each JSON object (or proplist if mochijson2 is used) within a list comprehension. I can use the delete function of proplists. But I am unsuccessful when trying to do that within a list comprehension.
Here is a bit code for context :
A = <<"[{\"id\": \"0129\", \"name\": \"joe\", \"photo\": \"joe.jpg\" }, {\"id\": \"0759\", \"name\": \"jane\", \"photo\": \"jane.jpg\" }, {\"id\": \"0929\", \"name\": \"john\", \"photo\": \"john.jpg\" }]">>.
Struct = mochijson2:decode(A).
{struct, JsonData} = Struct,
{struct, Id} = proplists:get_value(<<"id">>, JsonData),
Any suggestions illustrated with code much appreciated.
You can use lists:keydelete(Key, N, TupleList) to return a new tuple list with certain tuples removed. So in the list comprehension, for each entry extract the tuple lists (or proplists), and create a new struct with the key removed:
B = [{struct, lists:keydelete(<<"name">>, 1, Props)} || {struct, Props} <- Struct].
gives:
[{struct,[{<<"id">>,<<"0129">>},
{<<"photo">>,<<"joe.jpg">>}]},
{struct,[{<<"id">>,<<"0759">>},
{<<"photo">>,<<"jane.jpg">>}]},
{struct,[{<<"id">>,<<"0929">>},
{<<"photo">>,<<"john.jpg">>}]}]
and
iolist_to_binary(mochijson2:encode(B)).
gives:
<<"[{\"id\":\"0129\",\"photo\":\"joe.jpg\"},{\"id\":\"0759\",\"photo\":\"jane.jpg\"},{\"id\":\"0929\",\"photo\":\"john.jpg\"}]">>
By the way, using the lists/* tuple lists functions are much faster, but sometimes slightly less convenient than the proplists/* functions: http://sergioveiga.com/index.php/2010/05/14/erlang-listskeyfind-vs-proplistsget_value/