redis/redis-rb · error · ArgumentError

fields must not be empty

Error message

fields must not be empty

What it means

himport_prepare registers a named fieldset for the HIMPORT command family as per-connection session state on the server. After flattening its *fields argument it requires at least one field name; an empty list — no arguments, a single empty array, or an empty computed list — raises ArgumentError 'fields must not be empty' client-side.

Source

Thrown at lib/redis/commands/hashes.rb:492

      # other connections. See the README "Bulk hash ingestion (HIMPORT)"
      # section for connection-scoping guidance. Re-preparing an existing
      # +fieldset_name+ silently replaces it. Field order is preserved as
      # given; it defines the positional pairing used by #himport_set.
      #
      # @note HIMPORT support is experimental: the client API may change in a
      #   future minor release without a major version bump.
      #
      # @example
      #   redis.himport_prepare("shared", ["name", "email", "age"])
      #     # => "OK"
      #
      # @param [String] fieldset_name name used by later SET and DISCARD calls
      # @param [String, Array<String>] fields one or more field names
      # @return [String] `"OK"`
      # @api experimental
      def himport_prepare(fieldset_name, *fields)
        fields.flatten!(1)
        raise ArgumentError, "fields must not be empty" if fields.empty?

        send_command([:himport, "PREPARE", fieldset_name].concat(fields))
      end

      # Create or fully replace the hash at +key+ using the field list
      # registered under +fieldset_name+ on this connection. Values pair
      # positionally with the fields given to #himport_prepare; the value
      # count must equal the field count.
      #
      # The fieldset must exist on the executing connection, otherwise the
      # server replies with a "no such fieldset" error.
      #
      # @note HIMPORT support is experimental: the client API may change in a
      #   future minor release without a major version bump.
      #
      # @example
      #   redis.himport_set("shared:1", "shared", ["alice", "alice@example.com", "25"])
      #     # => "OK"

View on GitHub (pinned to 2ba9010b91)

Solutions

1. Pass at least one field: redis.himport_prepare('shared', 'name', 'email') or an array like redis.himport_prepare('shared', %w[name email])
2. Guard dynamic lists at the construction site and raise a domain-specific error naming the empty source
3. Remember fieldsets are per-connection state: after reconnect/failover re-prepare (the client auto-repairs via himport_auto_prepare unless disabled)

Example fix

# before
fields = []  # e.g. computed from user input
redis.himport_prepare('shared', fields)  # ArgumentError

# after
raise ArgumentError, 'no fields selected' if fields.empty?
redis.himport_prepare('shared', *fields)

fields = Array(fields).flatten
raise ArgumentError, 'no fields to register' if fields.empty?
redis.himport_prepare(fieldset_name, *fields)

When it happens

Trigger: redis.himport_prepare('schema') with no fields; redis.himport_prepare('schema', []); a fields array built at runtime (e.g. columns.select { ... }) that matched nothing and flattens to [].

Common situations: Dynamic schemas derived from model attributes or query results that can legitimately be empty; refactoring a fixed field list into a variable without adding a guard.

Related errors

• count argument must be specified
• wrong number of arguments
• ranges must be given as start/stop pairs
• logic must be :and or :or
• value is required for the MATCH operation

AI-assisted analysis of redis/redis-rb@2ba9010b91 (2026-08-23). Data as JSON: /api/errors/a74d72aac28c0a0c. Report an issue: GitHub.