converting slice of items into nested array
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aa...@pop42.com
Dec 7, 2016, 1:02:58 PM12/7/16
to golang-nuts
I'm pretty new to golang and struggling a bit with converting flat database results into a nested JSON object.
As an example... I have
type item struct {
raceID string
racename string
name string
votes int32
}
type race struct {
raceID string
racename string
racers
}
type racers []racer
type racer struct {
name string
votes int32
}
[]item is what I get back from my db query and I want to convert it into a json object that matches the race struct.
basically I want to convert
items := []item{
item{"1", "racename1", "scooby", 1000},
item{"1", "racename1", "scrappy", 9000},
item{"1", "racename1", "shaggy", 1000},
item{"2", "racename2", "shaggy", 450},
item{"2", "racename2", "fred", 550},
}
into something like
[{
"raceID": "1",
"racename": "racename1",
"racers": [{
"name": "scooby",
"votes": 1000
}, {
"name": "scrappy",
"votes": 9000
}, {
"name": "shaggy",
"votes": 1000
}]
}, {
"raceID": "2",
"racename": "racename2",
"racers": [{
"name": "shaggy",
"votes": 450
}, {
"name": "fred",
"votes": 550
}]
}]
I'm pretty sure I need to use maps and append some slices... but any pointing in the right direction would surely be appreciated.
Mikael Gustavsson
Dec 8, 2016, 3:55:27 AM12/8/16
to golang-nuts
There's no need to use maps, you want to follow this pattern:
for i := range items {
if i==0 || !grouped(i-1, i) {
appendToResult
}
appendToGroup
}
Here's the full example: https://play.golang.org/p/1e0rDDmq7b
Marvin Renich
Dec 8, 2016, 8:22:25 AM12/8/16
to golang-nuts
* Mikael Gustavsson <slv...@gmail.com> [161208 03:55]:
Note that this only works if the input slice is sorted, which it is in
the example data given by the OP, but that constraint was not explicitly
stated. If the input is not sorted, you must either sort it first, use
a map, or perform a search in each iteration.
If the input data is not guaranteed to be sorted, minimal changes to the
above would work: https://play.golang.org/p/4GsVUV_fBs
The map is only used to perform the search efficiently, and is no longer
used after the for loop.
...Marvin
the example data given by the OP, but that constraint was not explicitly
stated. If the input is not sorted, you must either sort it first, use
a map, or perform a search in each iteration.
If the input data is not guaranteed to be sorted, minimal changes to the
above would work: https://play.golang.org/p/4GsVUV_fBs
The map is only used to perform the search efficiently, and is no longer
used after the for loop.
...Marvin
Tamás Gulácsi
Dec 8, 2016, 9:31:24 AM12/8/16
to golang-nuts
Use capitalized field names and struct tags - lowercase is not exported, encoding/json does not see it.
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