Storage migration of elections-phragmen

srml/elections-phragmen/Cargo.toml

@@ -5,9 +5,7 @@ authors = ["Parity Technologies <[email protected]>"]
 edition = "2018"
 
 [dependencies]
-serde = { version = "1.0.101", optional = true }
 codec = { package = "parity-scale-codec", version = "1.0.0", default-features = false, features = ["derive"] }
-primitives = { package = "substrate-primitives",  path = "../../core/primitives", default-features = false }
 runtime_io = { package = "sr-io", path = "../../core/sr-io", default-features = false }
 sr-primitives = { path = "../../core/sr-primitives", default-features = false }
 phragmen = { package = "substrate-phragmen", path = "../../core/phragmen", default-features = false }
@@ -18,13 +16,13 @@ rstd = { package = "sr-std", path = "../../core/sr-std", default-features = fals
 [dev-dependencies]
 hex-literal = "0.2.1"
 balances = { package = "srml-balances", path = "../balances" }
+primitives = { package = "substrate-primitives",  path = "../../core/primitives" }
+serde = { version = "1.0.101" }
 
 [features]
 default = ["std"]
 std = [
 	"codec/std",
-	"primitives/std",
-	"serde",
 	"runtime_io/std",
 	"srml-support/std",
 	"sr-primitives/std",

srml/elections-phragmen/src/lib.rs

@@ -77,15 +77,18 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 
 use rstd::prelude::*;
+use codec::Decode;
 use sr_primitives::{print, traits::{Zero, StaticLookup, Bounded, Convert}};
 use sr_primitives::weights::SimpleDispatchInfo;
 use srml_support::{
 	decl_storage, decl_event, ensure, decl_module, dispatch,
+	storage::hashed::get_raw,
 	traits::{
 		Currency, Get, LockableCurrency, LockIdentifier, ReservableCurrency, WithdrawReasons,
 		ChangeMembers, OnUnbalanced, WithdrawReason
 	}
 };
+use runtime_io::twox_128;
 use phragmen::ExtendedBalance;
 use system::{self, ensure_signed, ensure_root};
 
@@ -159,6 +162,11 @@ decl_storage! {
 		/// The present candidate list. Sorted based on account id. A current member can never enter
 		/// this vector and is always implicitly assumed to be a candidate.
 		pub Candidates get(fn candidates): Vec<T::AccountId>;
+
+		/// Has the storage format been updated?
+		/// NOTE: Only use and set to false if you have used an early version of this module. Should
+		/// be set to true otherwise.
+		pub DidUpdate: bool = false;
 	}
 }
 
@@ -373,6 +381,10 @@ decl_module! {
 
 		/// What to do at the end of each block. Checks if an election needs to happen or not.
 		fn on_initialize(n: T::BlockNumber) {
+			if !DidUpdate::get() {
+				DidUpdate::put(true);
+				Self::do_update();
+			}
 			if let Err(e) = Self::end_block(n) {
 				print("Guru meditation");
 				print(e);
@@ -626,6 +638,36 @@ impl<T: Trait> Module<T> {
 
 		ElectionRounds::mutate(|v| *v += 1);
 	}
+
+	/// Perform the storage update needed to migrate the module from the initial version of the
+	/// storage.
+	///
+	/// If decoding the old storage fails in any way, the consequence is that we start with an empty
+	/// set.
+	fn do_update() {
+		let members_key = "PhragmenElection Members";
+		let runners_key = "PhragmenElection RunnersUp";
+
+		// old storage format.
+		let old_members: Vec<T::AccountId> = get_raw(&twox_128, members_key.as_bytes())
+			.map_or_else(|| vec![], |bytes| Decode::decode(&mut &*bytes).unwrap_or_default());
+		let old_runners: Vec<T::AccountId> = get_raw(&twox_128, runners_key.as_bytes())
+			.map_or_else(|| vec![], |bytes| Decode::decode(&mut &*bytes).unwrap_or_default());
+
+		// new storage format.
+		let new_runners: Vec<(T::AccountId, BalanceOf<T>)> = old_runners
+			.into_iter()
+			.map(|r| (r, Zero::zero()))
+			.collect();
+		let new_members: Vec<(T::AccountId, BalanceOf<T>)> = old_members
+			.into_iter()
+			.map(|r| (r, Zero::zero()))
+			.collect();
+
+		<Members<T>>::put(new_members);
+		<RunnersUp<T>>::put(new_runners);
+
+	}
 }
 
 #[cfg(test)]