Schema toml format doesn't describe how to specify indexes

[deontologician]

If you create a horizon app using --auto-create-collection and --auto-create-indexes, and then do hz get-schema on it, you will get stuff that looks like:

[collections.test_data]
indexes = ["a","a_b","a_c","a_id","abracadabra","b","field","id_$hz\\_v$","score","time","value_time"]

These index names have a particular format that tells horizon how to create the index when it's passed back to set-schema, but this isn't documented anywhere. We should document it so people are able to specify their indexes without needing to have horizon autogenerate them first.

@Tryneus can probably give us exact details on how the mapping works

[SenerDemiral]

Still
Uncaught Error: Collection "react_messages" has no index matching ["datetime"]

Example react-chat-app
Steps to produce

$ rethinkdb
$ cd reactChat
$ hz set-schema schema.toml

$ hz get-schema

# This is a TOML document
[collections.react_messages]
indexes = ["datetime"]
[groups.admin]
[groups.admin.rules.carte_blanche]
template = "any()"

$ hz serve --permissions no

Browse localhost:8181
Console message
Uncaught Error: Collection "react_messages" has no index matching ["datetime"]

RethinkDB Administration Console
r.db('reactChat').table('react_messages_17d5d480f158').info()
returned row

{
    "db": {
        "id":  "4348c660-469c-45cb-a4f7-748d25c5a6c1" ,
        "name":  "reactChat" ,
        "type":  "DB"
    } ,
    "doc_count_estimates": [
        24
    ] ,
    "id":  "6a5a7363-20c7-4646-876e-512c593b988d" ,
    "indexes": [
        "datetime"
    ] ,
    "name":  "react_messages_17d5d480f158" ,
    "primary_key":  "id" ,
    "type":  "TABLE"
}

schema.toml file

[collections.react_messages]
indexes = ["datetime"]

config.toml file

bind = [ "localhost" ]
port = 8181
secure = false
project_name = "reactChat"
serve_static = "dist"
auto_create_collection = true
connect = "localhost:28015"
start_rethinkdb = false
debug = true
token_secret = "vpd6iG3Ejfwdo5Fhuv16R3+J6fL69q5skGEkUEgXmb3tYGUy8YMDrwBgrkDeHPX4HKHT5Zrz1KPkhki0R009xA=="
allow_unauthenticated = true

[danielmewes]

@SenerDemiral This is an issue about documentation. There is a different tracker for issues with Horizon itself. I moved your comment over to there: rethinkdb/horizon#533

[Tryneus]

The current format is each field in the index, concatenated in order, delimited by underscores. Undescores and backslashes in field names are escaped with backslashes.

Examples:

index fields	index name
[ 'a', 'b', 'c' ]	a_b_c
[ 'foo_bar', 'baz' ]	foo\_bar_baz
[ 'x\y' ]	x\\y

There is an open issue to replace the naming scheme with JSON names, which will be a bit more readable and allows nested fields to be indexed: rethinkdb/horizon#444