ArangoDB唯一索引驗證

Question

快速問題：在ArangoDB中，如果我創建一個唯一索引（例如，一個唯一的哈希索引），ArangoDB是否會驗證該屬性的唯一性，還是只是因為我告訴過它唯一性而假設它是唯一的？ 我很好奇我是否應該在創建唯一索引之前執行驗證步驟來驗證數據的唯一性。

Answer 1

如您所知，ArangoDB會在使用索引之前先建立索引。 如果無法確保唯一性，它將引發異常：

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

與嘗試插入違反唯一約束的文檔時的操作類似：

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

因此，如果在創建索引之前在應用程序安裝過程中插入文檔（出於性能的考慮，這是一種可行的方法），則在以后創建這些索引時需要處理可能的異常。