1.7 KiB
@brief 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 will will 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 all
specified index attributes are null. Such documents will not be taken into account
for uniqueness checks.
In a non-sparse index, all documents regardless of null - attributes will be
indexed and will be taken into account for uniqueness checks.
In case that the index was successfully created, an object with the index details, including the index-identifier, is returned.
@EXAMPLE_ARANGOSH_OUTPUT{ensureUniqueConstraint} ~db._create("test"); db.test.ensureIndex({ type: "hash", fields: [ "a", "b.c" ], unique: true }); db.test.save({ a : 1, b : { c : 1 } }); db.test.save({ a : 1, b : { c : 1 } }); // xpError(ERROR_ARANGO_UNIQUE_CONSTRAINT_VIOLATED) db.test.save({ a : 1, b : { c : null } }); db.test.save({ a : 1 }); // xpError(ERROR_ARANGO_UNIQUE_CONSTRAINT_VIOLATED) ~db._drop("test"); @END_EXAMPLE_ARANGOSH_OUTPUT