Hash Indexes

    Creating a new document or updating a document will fail if the uniqueness is violated. If the index is declared sparse, a document will be excluded from the index and no uniqueness checks will be performed if any index attribute value is not set or has a value of .

    Ensures that a unique constraint exists:collection.ensureIndex({ type: "hash", fields: [ "field1", …, "fieldn" ], unique: true })

    Creates a unique hash index on all documents using field1, … _fieldn_as attribute paths. At least one attribute path has to be given.The index will be non-sparse by default.

    All documents in the collection must differ in terms of the indexed attributes. Creating a new document or updating an existing document willwill fail if the attribute uniqueness is violated.

    To create a sparse unique index, set the sparse attribute to true:

    collection.ensureIndex({ type: "hash", fields: [ "field1", …, "fieldn" ], unique: true, sparse: true })

    In case that the index was successfully created, the index identifier is returned.

    Non-existing attributes will default to null.In a sparse index all documents will be excluded from the index for which allspecified index attributes are null. Such documents will not be taken into accountfor uniqueness checks.

    In a non-sparse index, all documents regardless of null - attributes will beindexed and will be taken into account for uniqueness checks.

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    1. { 
    2.   "deduplicate" : true, 
    3.   "fields" : [ 
    4.     "a", 
    5.     "b.c" 
    6.   ], 
    7.   "id" : "test/16330", 
    8.   "isNewlyCreated" : true, 
    9.   "selectivityEstimate" : 1, 
    10.   "sparse" : false, 
    11.   "type" : "hash", 
    12.   "unique" : true, 
    13.   "code" : 201 
    14. }
    15. { 
    16.   "_id" : "test/16333", 
    17.   "_key" : "16333", 
    18.   "_rev" : "_ZHpYszy--_" 
    19. }
    20. [ArangoError 1210: unique constraint violated - in index 16330 of type hash over ["a","b.c"]; conflicting key: 16333]
    21. { 
    22.   "_id" : "test/16339", 
    23.   "_rev" : "_ZHpYsz6--_" 
    24. }
    25. [ArangoError 1210: unique constraint violated - in index 16330 of type hash over ["a","b.c"]; conflicting key: 16339]

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    Ensures that a non-unique hash index exists:collection.ensureIndex({ type: "hash", fields: [ "field1", …, "fieldn" ] })

    Creates a non-unique hash index on all documents using field1, … _fieldn_as attribute paths. At least one attribute path has to be given.The index will be non-sparse by default.

    To create a sparse unique index, set the sparse attribute to true:

    In case that the index was successfully created, an object with the indexdetails, including the index-identifier, is returned.

    Show execution results

    1. { 
    2.   "deduplicate" : true, 
    3.   "fields" : [ 
    4.     "a" 
    5.   ], 
    6.   "id" : "test/16233", 
    7.   "isNewlyCreated" : true, 
    8.   "selectivityEstimate" : 1, 
    9.   "sparse" : false, 
    10.   "type" : "hash", 
    11.   "unique" : false, 
    12.   "code" : 201 
    13. }
    14. { 
    15.   "_id" : "test/16236", 
    16.   "_key" : "16236", 
    17.   "_rev" : "_ZHpYsf2--_" 
    18. }
    19. { 
    20.   "_id" : "test/16240", 
    21.   "_key" : "16240", 
    22.   "_rev" : "_ZHpYsf6--_" 
    23. }
    24. { 
    25.   "_id" : "test/16243", 
    26.   "_rev" : "_ZHpYsf6--B" 
    27. }

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    Creates a non-unique hash array index for the individual elements of the arrayattributes field1[], … fieldn[] found in the documents. At leastone attribute path has to be given. The index always treats the indexed arrays assparse.

    It is possible to combine array indexing with standard indexing:collection.ensureIndex({ type: "hash", fields: [ "field1[*]", "field2" ] })

    In case that the index was successfully created, an object with the indexdetails, including the index-identifier, is returned.

    Show execution results

    1. { 
    2.   "deduplicate" : true, 
    3.   "fields" : [ 
    4.     "a[*]" 
    5.   ], 
    6.   "id" : "test/16250", 
    7.   "isNewlyCreated" : true, 
    8.   "selectivityEstimate" : 1, 
    9.   "sparse" : false, 
    10.   "type" : "hash", 
    11.   "unique" : false, 
    12.   "code" : 201 
    13. }
    14. { 
    15.   "_id" : "test/16253", 
    16.   "_key" : "16253", 
    17.   "_rev" : "_ZHpYsi2--_" 
    18. }
    19. { 
    20.   "_id" : "test/16257", 
    21.   "_key" : "16257", 
    22.   "_rev" : "_ZHpYsi2--B" 
    23. }
    24. { 
    25.   "_id" : "test/16260", 
    26.   "_key" : "16260", 
    27. }

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    It is possible to create secondary indexes using the edge attributes _fromand _to, starting with ArangoDB 3.0. A combined index over both fields togetherwith the unique option enabled can be used to prevent duplicate relations frombeing created.

    For example, a document collection verts might contain vertices with the documenthandles verts/A, and verts/C. Relations between these documents canbe stored in an edge collection edges for instance. Now, you may want to make surethat the vertex verts/A is never linked to verts/B by an edge more than once.This can be achieved by adding a unique, non-sparse hash index for the fields _fromand _to:

    Creating an edge { from: "verts/A", _to: "verts/B" } in _edges will be accepted,but only once. Another attempt to store an edge with the relation A → B willbe rejected by the server with a unique constraint violated error. This includesupdates to the _from and _to fields.

    Note that adding a relation B → A is still possible, so is A → Aand B → B, because they are all different relations in a directed graph.Each one can only occur once however.