pallet进阶(8)-offchain storage

链下存储
顾名思义，链下存储不保存在链上，而是保存在节点本地的。

1. 案例1-链下存储基本操作

在ocw中使用StorageValueRef
pallet的lib.rs中

#![cfg_attr(not(feature = "std"), no_std)]

pub use pallet::*;
#[frame_support::pallet]
pub mod pallet {
  use frame_support::pallet_prelude::*;
  use frame_system::pallet_prelude::*;

  use sp_runtime::offchain::storage::{
    MutateStorageError, StorageRetrievalError, StorageValueRef,
  };

  #[pallet::pallet]
  #[pallet::generate_store(pub(super) trait Store)]
  pub struct Pallet<T>(_);

  #[pallet::config]
  pub trait Config: frame_system::Config {}

  #[pallet::hooks]
  impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
    fn offchain_worker(block_number: T::BlockNumber) {
      if Self::should_print() {
        log::info!(target:"offchain-storage", "1. Block number: {:?}, should print +++++++++++++++++++++++++++ ", block_number);
      } else {
        log::info!(target:"offchain-storage", "2. Block number: {:?}, Should not print +++++++++++++++++++++++++++ ", block_number);
      }
    }
  }

  //内部方法  
  impl<T: Config> Pallet<T> {
    fn should_print() -> bool {
      const LAST_VALUE: () = ();
      //重点看这里
      let val = StorageValueRef::persistent(b"ocw-demo::last_value");
      let res = val.mutate(
          |last_flag: Result<Option<bool>, StorageRetrievalError>| match last_flag {
            Ok(Some(flag)) => Ok(!flag),
            _ => Ok(true),
          },
        );

      match res {
        Ok(flag) => flag,
        Err(MutateStorageError::ValueFunctionFailed(LAST_VALUE)) => false,
        Err(MutateStorageError::ConcurrentModification(_)) => false,
      }
    }
  }
}

相关引入和编译后，即可正常运行

2. 在ocw中使用local_storage_set/get

手动通过rpc对storage demo::flag设置为true，然后在代码中查看此存储的值，然后再将此值写到另外一个存储demo::result中

#![cfg_attr(not(feature = "std"), no_std)]

pub use pallet::*;
#[frame_support::pallet]
pub mod pallet {
  use frame_support::pallet_prelude::*;
  use frame_system::pallet_prelude::*;

  extern crate alloc;
  use alloc::string::{String, ToString};

  #[pallet::pallet]
  #[pallet::generate_store(pub(super) trait Store)]
  pub struct Pallet<T>(_);

  #[pallet::config]
  pub trait Config: frame_system::Config {}

  #[pallet::hooks]
  impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
    fn offchain_worker(block_number: T::BlockNumber) {
      let flag = Self::should_print();

      if flag {
        log::info!(target:"offchain-storage2222", "1. Offchain-storage2, block number: {:?}, should print +++++++++++ ", block_number);
      } else {
        log::info!(target:"offchain-storage2222", "2. Offchain-storage2, block number: {:?}, Should not print +++++++++++ ", block_number);
      }

      Self::set_result(flag);
    }
  }

  impl<T: Config> Pallet<T> {
    fn should_print() -> bool {
      let kind = sp_core::offchain::StorageKind::PERSISTENT;
      if let Some(flag) = sp_io::offchain::local_storage_get(kind, b"demo::flag") {
        let ret = match String::from_utf8(flag) {
          Ok(v) => v.eq(&"true"),
          Err(_) => false,
        };
        ret
      } else {
        false
      }
    }

    fn set_result(flag: bool) {
      let kind = sp_core::offchain::StorageKind::PERSISTENT;
      let value = match flag {
        true => "true".to_string(),
        false => "false".to_string(),
      };
      sp_io::offchain::local_storage_set(kind, b"demo::result", value.as_bytes());
    }
  }
}

总结

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