在 Solana 中实现映射表与嵌套映射表

本文将通过填充 seeds 参数，模拟 Solidity 中的映射（mapping）功能。seeds 中的数据类似于映射的键，用于生成唯一的数据账户地址。

以 Solidity 为例：

contract ExampleMapping {
    struct SomeNum { uint64 num; }
    mapping(uint64 => SomeNum) public exampleMap;

    function setExampleMap(uint64 key, uint64 val) public {
        exampleMap[key] = SomeNum(val);
    }
}

我们将在 Solana Anchor 中创建项目 example_map，实现类似功能。

---

初始化映射表

Rust 实现

首先展示初始化代码，引入新语法：

use anchor_lang::prelude::*;
use std::mem::size_of;

declare_id!("BB7Z6YvBMPRKDutbVh8SGy8QS82e9GZc4jLrEt1Ym2o9");

#[program]
pub mod example_map {
    use super::*;

    pub fn initialize(ctx: Context<Initialize>, key: u64) -> Result<()> {
        Ok(())
    }
}

#[derive(Accounts)]
#[instruction(key: u64)]
pub struct Initialize<'info> {
    #[account(
        init,
        payer = signer,
        space = size_of::<Val>() + 8,
        seeds = [&key.to_le_bytes()],
        bump
    )]
    val: Account<'info, Val>,
    #[account(mut)]
    signer: Signer<'info>,
    system_program: Program<'info, System>,
}

#[account]
pub struct Val {
    value: u64,
}

关键点解析

1. seeds = \&key.to_le_bytes() ：
   • seeds 需为字节数组，key（u64）通过 to_le_bytes() 转换为 8 字节小端数组（little-endian）。
   • 可选大端（to_be_bytes()），只需保持一致。
   • seeds 类似映射表的键，生成唯一的程序派生地址（PDA）。
2. #instruction(key: u64) ：
   • 使 initialize 的参数 key 在 Initialize 结构中可见，用于 seeds 计算。
   • 缺少此宏，init 将无法访问 key。

类比：seeds 中的 key 类似 mapping(uint64 => Val) 中的键。

Typescript 实现

初始化测试代码：

import * as anchor from "@coral-xyz/anchor";
import { Program } from "@coral-xyz/anchor";
import { ExampleMap } from "../target/types/example_map";

describe("example_map", () => {
  anchor.setProvider(anchor.AnchorProvider.env());

  const program = anchor.workspace.ExampleMap as Program<ExampleMap>;

  it("Initialize mapping storage", async () => {
    const key = new anchor.BN(42);

    const seeds = [key.toArrayLike(Buffer, "le", 8)];
    const [valueAccount, _bump] = anchor.web3.PublicKey.findProgramAddressSync(
      seeds,
      program.programId
    );

    await program.methods
      .initialize(key)
      .accounts({ val: valueAccount })
      .rpc();
  });
});

• key.toArrayLike(Buffer, "le", 8) 将 u64 转为 8 字节小端缓冲区，与 Rust 保持一致。
• 每个映射表项对应一个独立账户，需单独初始化。

---

设置映射表值

Rust 实现

新增 set 函数：

#[program]
pub mod example_map {
    use super::*;

    pub fn initialize(ctx: Context<Initialize>, key: u64) -> Result<()> {
        Ok(())
    }

    pub fn set(ctx: Context<Set>, key: u64, val: u64) -> Result<()> {
        ctx.accounts.val.value = val;
        Ok(())
    }
}

#[derive(Accounts)]
#[instruction(key: u64)]
pub struct Set<'info> {
    #[account(mut, seeds = [&key.to_le_bytes()], bump)]
    val: Account<'info, Val>,
}

• Set 使用相同 seeds 定位账户，mut 表示可写。

Typescript 读写

完整测试代码：

import * as anchor from "@coral-xyz/anchor";
import { Program } from "@coral-xyz/anchor";
import { ExampleMap } from "../target/types/example_map";

describe("example_map", () => {
  anchor.setProvider(anchor.AnchorProvider.env());

  const program = anchor.workspace.ExampleMap as Program<ExampleMap>;

  it("Initialize and set value", async () => {
    const key = new anchor.BN(42);
    const value = new anchor.BN(1337);

    const seeds = [key.toArrayLike(Buffer, "le", 8)];
    let valueAccount = anchor.web3.PublicKey.findProgramAddressSync(
      seeds,
      program.programId,
    )[0];

    await program.methods.initialize(key).accounts({ val: valueAccount }).rpc();

    await program.methods.set(key, value).accounts({ val: valueAccount }).rpc();

    let result = await program.account.val.fetch(valueAccount);

    console.log(`the value ${result.value} was stored in ${valueAccount.toBase58()}`);

  });
});

• 客户端通过 seeds 推导地址，读写语法与前文一致。

---

嵌套映射表解析

Solidity vs. 真实嵌套

• 真实嵌套（如 Python）：mapkey1 返回另一映射表。
• Solidity 嵌套：mapping(uint => mapping(uint => uint)) 需提供所有键（如 mapkey1key2）获取值，非真正嵌套。
• Solana 限制：seeds 模拟 Solidity 风格，需完整提供所有键。

Rust 实现

完整嵌套映射表代码：

use anchor_lang::prelude::*;
use std::mem::size_of;

declare_id!("BB7Z6YvBMPRKDutbVh8SGy8QS82e9GZc4jLrEt1Ym2o9");

#[program]
pub mod example_map {
    use super::*;

    pub fn initialize(ctx: Context<Initialize>, key1: u64, key2: u64) -> Result<()> {
        Ok(())
    }

    pub fn set(ctx: Context<Set>, key1: u64, key2: u64, val: u64) -> Result<()> {
        ctx.accounts.val.value = val;
        Ok(())
    }
}

#[derive(Accounts)]
#[instruction(key1: u64, key2: u64)]
pub struct Initialize<'info> {
    #[account(
        init,
        payer = signer,
        space = size_of::<Val>() + 8,
        seeds = [&key1.to_le_bytes(), &key2.to_le_bytes()],
        bump
    )]
    val: Account<'info, Val>,
    #[account(mut)]
    signer: Signer<'info>,
    system_program: Program<'info, System>,
}

#[derive(Accounts)]
#[instruction(key1: u64, key2: u64)]
pub struct Set<'info> {
    #[account(mut, seeds = [&key1.to_le_bytes(), &key2.to_le_bytes()], bump)]
    val: Account<'info, Val>,
}

#[account]
pub struct Val {
    value: u64,
}

• seeds 包含两个键，模拟 mapping(uint => mapping(uint => uint))。

Typescript 实现

import * as anchor from "@coral-xyz/anchor";
import { Program } from "@coral-xyz/anchor";
import { ExampleMap } from "../target/types/example_map";

describe("example_map", () => {
  anchor.setProvider(anchor.AnchorProvider.env());

  const program = anchor.workspace.ExampleMap as Program<ExampleMap>;

  it("Initialize and set value", async () => {
    const key1 = new anchor.BN(42);
    const key2 = new anchor.BN(43);
    const value = new anchor.BN(1337);

    const seeds = [key1.toArrayLike(Buffer, "le", 8), key2.toArrayLike(Buffer, "le", 8)];
    let valueAccount = anchor.web3.PublicKey.findProgramAddressSync(
      seeds,
      program.programId,
    )[0];

    await program.methods.initialize(key1, key2).accounts({val: valueAccount}).rpc();
    await program.methods.set(key1, key2, value).accounts({val: valueAccount}).rpc();

    let result = await program.account.val.fetch(valueAccount);
    console.log(`the value ${result.value} was stored in ${valueAccount.toBase58()}`);

  });
});

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