{"id":1791,"date":"2022-11-08T10:10:56","date_gmt":"2022-11-08T08:10:56","guid":{"rendered":"https:\/\/www.netexpertise.eu\/en\/?p=1791"},"modified":"2022-11-13T21:12:49","modified_gmt":"2022-11-13T19:12:49","slug":"turn-a-terraform-map-of-maps-into-a-single-map","status":"publish","type":"post","link":"http:\/\/www.netexpertise.eu\/en\/devops\/terraform\/turn-a-terraform-map-of-maps-into-a-single-map.html","title":{"rendered":"Turn a Terraform Map of Maps into a Single Map…"},"content":{"rendered":"\n

…Or how to avoid the ‘Call to function “merge” failed: arguments must be maps or objects, got “tuple”.’<\/em> error message. Maps of maps example.

<\/p>\n\n\n\n

\"maps<\/figure>\n\n\n\n


Issue Producing a Single Map<\/h2>\n\n\n\n


Here’s a typical 2 level data structure that fits users in subgroups, themselves belonging to departments:<\/p>\n\n\n\n

locals {\n   groups = {\n      it = {\n         admin   = [\"it1\",\"it2\"]\n         editors = [\"it3\",\"it4\"]\n      },\n      accounts = {\n         editors = [\"account1\",\"account2\"]\n         viewers = [\"account3\",\"account4\"]\n      }\n   }\n}<\/code><\/pre>\n\n\n\n

There are good chances you will need to flatten that structure to create some Terraform<\/a> ressources.
Our target is a map of unique subgroups department_subgroup = [ “user1”, “user2” ]. In our example:<\/p>\n\n\n\n
subgroups = {\n  \"accounts_editors\" = [\n    \"account1\",\n    \"account2\",\n  ]\n  \"accounts_viewers\" = [\n    \"account3\",\n    \"account4\",\n  ]\n  \"it_admin\" = [\n    \"it1\",\n    \"it2\",\n  ]\n  \"it_editors\" = [\n    \"it3\",\n    \"it4\",\n  ]\n}<\/code><\/pre>\n\n\n\n

It is pretty simple to get a list of distinct maps flattening the resulting lists of a double loop:<\/p>\n\n\n\n
subgroups = flatten([\n   for group,subgroups in local.groups : [\n      for subgroup, users in subgroups : {\n         \"${group}_${subgroup}\" = users\n      }\n   ]\n])\n# output:\nsubgroups = [\n  {\n    \"accounts_editors\" = [\n      \"account1\",\n      \"account2\",\n    ]\n  },\n  {\n    \"accounts_viewers\" = [\n      \"account3\",\n      \"account4\",\n    ]\n  },\n  {\n    \"it_admin\" = [\n      \"it1\",\n      \"it2\",\n    ]\n  },\n  {\n    \"it_editors\" = [\n      \"it3\",\n      \"it4\",\n    ]\n  },\n]<\/code><\/pre>\n\n\n\n
All we need is merge these maps into a single map but if we do, we end up with:
‘Call to function “merge” failed: arguments must be maps or objects, got “tuple”.’<\/em>

<\/p>\n\n\n\n
\"Call
Call to function “merge” failed: arguments must be maps or objects, got “tuple”<\/em><\/figcaption><\/figure>\n\n\n\n

2 ways to the rescue: the ugly and the elegant.<\/p>\n\n\n\n

The Ugly Way : Another Terraform Loop<\/h2>\n\n\n\n

The first way you can think of is to process the new map through another for<\/a> loop. That makes 3 loops and does not make any sense since a simple merge would do the job. Each map has one element only, so we take the first key and first value.<\/p>\n\n\n\n
subgroups = { for subgroup in flatten([\n   for group,subgroups in local.groups : [\n      for subgroup, users in subgroups : {\n         \"${group}_${subgroup}\" = users\n      }\n   ]\n]) : keys(subgroup)[0] => values(subgroup)[0] }<\/code><\/pre>\n\n\n\n

The Elegant Way : Function Expansion<\/h2>\n\n\n\n

This is much shorter than above solution:<\/p>\n\n\n\n
subgroups = merge(flatten([\n   for group,subgroups in local.groups : [\n      for subgroup, users in subgroups : {\n         \"${group}_${subgroup}\" = users\n      }\n   ]\n])...)<\/code><\/pre>\n\n\n\n
The result is exactly the same but what has changed? Just the 3 dots…
Expansion<\/a> takes each element out of a list and pass them on to the calling function.
<\/p>\n","protected":false},"excerpt":{"rendered":"
…Or how to avoid the ‘Call to function “merge” failed: arguments must be maps or objects, got “tuple”.’ error message. Maps of maps example. Issue Producing a Single Map Here’s a typical 2 level data structure that fits users in subgroups, themselves belonging to departments: There are good chances you will need to flatten that […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0},"categories":[425,452],"tags":[453],"yoast_head":"\nNetexpertise - Turn a Terraform Map of Maps into a Single Map...<\/title>\n<meta name=\"description\" content=\"Build Terraform single maps from multi-level maps with for loops and merge function expansion\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.netexpertise.eu\/en\/devops\/terraform\/turn-a-terraform-map-of-maps-into-a-single-map.html\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Netexpertise - 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