Quick question: in ArangoDB, if I create a unique index (for example a unique hash index), does ArangoDB validate the uniqueness of that attribute, or just assume it because I told it it's unique? I'm curious if I should go through a validation step to verify the uniqueness of my data before creating unique indices.
1 Answers
3
votes
As you know ArangoDB builds up the indexes before you can use them. If it fails to ensure the uniqueness, it will throw an exception:
127.0.0.1:8529@_system> c = db._create("c")
[ArangoCollection 169, "c" (type document, status loaded)]
127.0.0.1:8529@_system> c.insert({"abc":1})
{
"_id" : "c/172",
"_key" : "172",
"_rev" : "_T1m73_m---"
}
127.0.0.1:8529@_system> c.insert({"abc":1})
{
"_id" : "c/176",
"_key" : "176",
"_rev" : "_T1m748K---"
}
127.0.0.1:8529@_system> c.ensureIndex(
...> {"type":"hash","unique":true,"fields":["abc"]})
JavaScript exception in file '.../arangosh.js' at 97,7:
ArangoError 1210: unique constraint violated
! throw error;
! ^
stacktrace: ArangoError: unique constraint violated
at Object.exports.checkRequestResult (.../arangosh.js:95:21)
at ArangoCollection.ensureIndex (.../arango-collection.js:733:12)
at <shell command>:1:3
127.0.0.1:8529@_system> c.ensureIndex(
...> {"type":"skiplist","unique":true,"fields":["abc"]})
JavaScript exception in file '.../arangosh.js' at 97,7:
ArangoError 1210: unique constraint violated
! throw error;
! ^
stacktrace: ArangoError: unique constraint violated
at Object.exports.checkRequestResult (.../arangosh.js:95:21)
at ArangoCollection.ensureIndex (.../arango-collection.js:733:12)
at <shell command>:1:3
Similar to what it does if you try to insert a document that violates the unique constraint:
127.0.0.1:8529@_system> db._drop("c")
127.0.0.1:8529@_system> c = db._create("c")
[ArangoCollection 315, "c" (type document, status loaded)]
127.0.0.1:8529@_system> c.ensureIndex({
...>"type":"skiplist","unique":true,"fields":["abc"]})
{
"id" : "c/318",
"type" : "skiplist",
"fields" : [
"abc"
],
"unique" : true,
"sparse" : false,
"isNewlyCreated" : true,
"code" : 201
}
127.0.0.1:8529@_system> c.insert({"abc":1})
{
"_id" : "c/330",
"_key" : "330",
"_rev" : "_T1n-B2S---"
}
127.0.0.1:8529@_system> c.insert({"abc":1})
JavaScript exception in file '.../arangosh.js' at 97,7:
ArangoError 1210: cannot create document, unique constraint violated
! throw error;
! ^
stacktrace: ArangoError: cannot create document, unique constraint violated
at Object.exports.checkRequestResult (.../arangosh.js:95:21)
at ArangoCollection.save.ArangoCollection.insert
(.../arango-collection.js:978:14)
at <shell command>:1:3
So if you insert your documents during your application setup before creating the index (for performance reasons a viable approach) you need to handle possible exceptions when creating these indices afterwards.
