HsetnxCommand
HSETNX _key_ _field_ _value_ (Redis >
1.3.10)= Time complexity: O(1)Set the specified hash field to the specified value, if field does not exist yet.
If key does not exist, a new key holding a hash is created.
If the field already exists, this operation has no effect and returns 0.Otherwise, the field is set to value and the operation returns 1.