Cosmos Dev Series: Cosmos-SDK-based Blockchain Upgrade - x/foo migration impl

migrations.go

package v2 // migrations.go

func UpdateParams(ctx sdk.Context, paramStore *paramtypes.Subspace) error {
    ...
    paramStore.Set(ctx, types.KeyValue, "foobar")
  
    return nil
}

func MigrateStore(ctx sdk.Context, storeKey storetypes.StoreKey, cdc codec.BinaryCodec) error {
    store := ctx.KVStore(storeKey)
  
    return migrateValuesWithPrefix(store, cdc)
}

func migrateValuesWithPrefix(store sdk.KVStore, cdc codec.BinaryCodec) error {
    oldStoreIter := store.Iterator(nil, nil)
  
    for ; oldStoreIter.Valid(); oldStoreIter.Next() {
        oldKey := oldStoreIter.Key()
        oldVal := store.Get(oldKey)
      
        newKey, newVal := migrateValue(cdc, oldKey, oldVal)
        store.Set(newKey, newVal)
        store.Delete(oldKey) // Delete old key, value
    }
  
    return nil
}

func migrateValue(cdc codec.BinaryCodec, oldKey []byte, oldVal []byte) (newKey []byte, newVal []byte) {
    valWithMemo := types.ValueWithMemo{
        Value: string(oldVal),
        Memo:  "HELLO", // Default memo as 'HELLO'
    }
    newKey = types.GetValueKey(string(oldKey))
    newVal = cdc.MustMarshal(&valWithMemo)
    return
}