我可以使用 FlatBuffers 遍历所有 table 项吗？

Question

我有以下 FlatBuffers 模式（简化）：

table StringNode {
  prefix: StringNode;
  suffix: StringNode;
  value: string (required);
}

table NodesData {
  url1: StringNode (required);
  url2: StringNode (required);
  url3: StringNode (required);
}

root_type NodesData;

有没有一种方法可以迭代所有 StringNode 而无需单独 urls: [StringNode] 并在编码时添加它们？

我在生成的 Rust 代码中没有看到任何类似的东西。

PS。可以使用 flatc --rust filename 生成 Rust 代码。这是我拥有的：

// automatically generated by the FlatBuffers compiler, do not modify



use std::mem;
use std::cmp::Ordering;

extern crate flatbuffers;
use self::flatbuffers::{EndianScalar, Follow};

#[allow(unused_imports, dead_code)]
pub mod com {

  use std::mem;
  use std::cmp::Ordering;

  extern crate flatbuffers;
  use self::flatbuffers::{EndianScalar, Follow};
#[allow(unused_imports, dead_code)]
pub mod company {

  use std::mem;
  use std::cmp::Ordering;

  extern crate flatbuffers;
  use self::flatbuffers::{EndianScalar, Follow};
#[allow(unused_imports, dead_code)]
pub mod project {

  use std::mem;
  use std::cmp::Ordering;

  extern crate flatbuffers;
  use self::flatbuffers::{EndianScalar, Follow};
#[allow(unused_imports, dead_code)]
pub mod fb {

  use std::mem;
  use std::cmp::Ordering;

  extern crate flatbuffers;
  use self::flatbuffers::{EndianScalar, Follow};
#[allow(unused_imports, dead_code)]
pub mod node {

  use std::mem;
  use std::cmp::Ordering;

  extern crate flatbuffers;
  use self::flatbuffers::{EndianScalar, Follow};

pub enum StringNodeOffset {}
#[derive(Copy, Clone, PartialEq)]

pub struct StringNode<'a> {
  pub _tab: flatbuffers::Table<'a>,
}

impl<'a> flatbuffers::Follow<'a> for StringNode<'a> {
    type Inner = StringNode<'a>;
    #[inline]
    fn follow(buf: &'a [u8], loc: usize) -> Self::Inner {
        Self { _tab: flatbuffers::Table { buf, loc } }
    }
}

impl<'a> StringNode<'a> {
    #[inline]
    pub fn init_from_table(table: flatbuffers::Table<'a>) -> Self {
        StringNode { _tab: table }
    }
    #[allow(unused_mut)]
    pub fn create<'bldr: 'args, 'args: 'mut_bldr, 'mut_bldr>(
        _fbb: &'mut_bldr mut flatbuffers::FlatBufferBuilder<'bldr>,
        args: &'args StringNodeArgs<'args>) -> flatbuffers::WIPOffset<StringNode<'bldr>> {
      let mut builder = StringNodeBuilder::new(_fbb);
      if let Some(x) = args.value { builder.add_value(x); }
      if let Some(x) = args.suffix { builder.add_suffix(x); }
      if let Some(x) = args.prefix { builder.add_prefix(x); }
      builder.finish()
    }

    pub const VT_PREFIX: flatbuffers::VOffsetT = 4;
    pub const VT_SUFFIX: flatbuffers::VOffsetT = 6;
    pub const VT_VALUE: flatbuffers::VOffsetT = 8;

  #[inline]
  pub fn prefix(&self) -> Option<StringNode<'a>> {
    self._tab.get::<flatbuffers::ForwardsUOffset<StringNode>>(StringNode::VT_PREFIX, None)
  }
  #[inline]
  pub fn suffix(&self) -> Option<StringNode<'a>> {
    self._tab.get::<flatbuffers::ForwardsUOffset<StringNode>>(StringNode::VT_SUFFIX, None)
  }
  #[inline]
  pub fn value(&self) -> &'a str {
    self._tab.get::<flatbuffers::ForwardsUOffset<&str>>(StringNode::VT_VALUE, None).unwrap()
  }
}

impl flatbuffers::Verifiable for StringNode<'_> {
  #[inline]
  fn run_verifier(
    v: &mut flatbuffers::Verifier, pos: usize
  ) -> Result<(), flatbuffers::InvalidFlatbuffer> {
    use self::flatbuffers::Verifiable;
    v.visit_table(pos)?
     .visit_field::<flatbuffers::ForwardsUOffset<StringNode>>(&"prefix", Self::VT_PREFIX, false)?
     .visit_field::<flatbuffers::ForwardsUOffset<StringNode>>(&"suffix", Self::VT_SUFFIX, false)?
     .visit_field::<flatbuffers::ForwardsUOffset<&str>>(&"value", Self::VT_VALUE, true)?
     .finish();
    Ok(())
  }
}
pub struct StringNodeArgs<'a> {
    pub prefix: Option<flatbuffers::WIPOffset<StringNode<'a>>>,
    pub suffix: Option<flatbuffers::WIPOffset<StringNode<'a>>>,
    pub value: Option<flatbuffers::WIPOffset<&'a str>>,
}
impl<'a> Default for StringNodeArgs<'a> {
    #[inline]
    fn default() -> Self {
        StringNodeArgs {
            prefix: None,
            suffix: None,
            value: None, // required field
        }
    }
}
pub struct StringNodeBuilder<'a: 'b, 'b> {
  fbb_: &'b mut flatbuffers::FlatBufferBuilder<'a>,
  start_: flatbuffers::WIPOffset<flatbuffers::TableUnfinishedWIPOffset>,
}
impl<'a: 'b, 'b> StringNodeBuilder<'a, 'b> {
  #[inline]
  pub fn add_prefix(&mut self, prefix: flatbuffers::WIPOffset<StringNode<'b >>) {
    self.fbb_.push_slot_always::<flatbuffers::WIPOffset<StringNode>>(StringNode::VT_PREFIX, prefix);
  }
  #[inline]
  pub fn add_suffix(&mut self, suffix: flatbuffers::WIPOffset<StringNode<'b >>) {
    self.fbb_.push_slot_always::<flatbuffers::WIPOffset<StringNode>>(StringNode::VT_SUFFIX, suffix);
  }
  #[inline]
  pub fn add_value(&mut self, value: flatbuffers::WIPOffset<&'b  str>) {
    self.fbb_.push_slot_always::<flatbuffers::WIPOffset<_>>(StringNode::VT_VALUE, value);
  }
  #[inline]
  pub fn new(_fbb: &'b mut flatbuffers::FlatBufferBuilder<'a>) -> StringNodeBuilder<'a, 'b> {
    let start = _fbb.start_table();
    StringNodeBuilder {
      fbb_: _fbb,
      start_: start,
    }
  }
  #[inline]
  pub fn finish(self) -> flatbuffers::WIPOffset<StringNode<'a>> {
    let o = self.fbb_.end_table(self.start_);
    self.fbb_.required(o, StringNode::VT_VALUE,"value");
    flatbuffers::WIPOffset::new(o.value())
  }
}

impl std::fmt::Debug for StringNode<'_> {
  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
    let mut ds = f.debug_struct("StringNode");
      ds.field("prefix", &self.prefix());
      ds.field("suffix", &self.suffix());
      ds.field("value", &self.value());
      ds.finish()
  }
}
pub enum NodesDataOffset {}
#[derive(Copy, Clone, PartialEq)]

pub struct NodesData<'a> {
  pub _tab: flatbuffers::Table<'a>,
}

impl<'a> flatbuffers::Follow<'a> for NodesData<'a> {
    type Inner = NodesData<'a>;
    #[inline]
    fn follow(buf: &'a [u8], loc: usize) -> Self::Inner {
        Self { _tab: flatbuffers::Table { buf, loc } }
    }
}

impl<'a> NodesData<'a> {
    #[inline]
    pub fn init_from_table(table: flatbuffers::Table<'a>) -> Self {
        NodesData { _tab: table }
    }
    #[allow(unused_mut)]
    pub fn create<'bldr: 'args, 'args: 'mut_bldr, 'mut_bldr>(
        _fbb: &'mut_bldr mut flatbuffers::FlatBufferBuilder<'bldr>,
        args: &'args NodesDataArgs<'args>) -> flatbuffers::WIPOffset<NodesData<'bldr>> {
      let mut builder = NodesDataBuilder::new(_fbb);
      if let Some(x) = args.url3 { builder.add_url3(x); }
      if let Some(x) = args.url2 { builder.add_url2(x); }
      if let Some(x) = args.url1 { builder.add_url1(x); }
      builder.finish()
    }

    pub const VT_URL1: flatbuffers::VOffsetT = 4;
    pub const VT_URL2: flatbuffers::VOffsetT = 6;
    pub const VT_URL3: flatbuffers::VOffsetT = 8;

  #[inline]
  pub fn url1(&self) -> StringNode<'a> {
    self._tab.get::<flatbuffers::ForwardsUOffset<StringNode>>(NodesData::VT_URL1, None).unwrap()
  }
  #[inline]
  pub fn url2(&self) -> StringNode<'a> {
    self._tab.get::<flatbuffers::ForwardsUOffset<StringNode>>(NodesData::VT_URL2, None).unwrap()
  }
  #[inline]
  pub fn url3(&self) -> StringNode<'a> {
    self._tab.get::<flatbuffers::ForwardsUOffset<StringNode>>(NodesData::VT_URL3, None).unwrap()
  }
}

impl flatbuffers::Verifiable for NodesData<'_> {
  #[inline]
  fn run_verifier(
    v: &mut flatbuffers::Verifier, pos: usize
  ) -> Result<(), flatbuffers::InvalidFlatbuffer> {
    use self::flatbuffers::Verifiable;
    v.visit_table(pos)?
     .visit_field::<flatbuffers::ForwardsUOffset<StringNode>>(&"url1", Self::VT_URL1, true)?
     .visit_field::<flatbuffers::ForwardsUOffset<StringNode>>(&"url2", Self::VT_URL2, true)?
     .visit_field::<flatbuffers::ForwardsUOffset<StringNode>>(&"url3", Self::VT_URL3, true)?
     .finish();
    Ok(())
  }
}
pub struct NodesDataArgs<'a> {
    pub url1: Option<flatbuffers::WIPOffset<StringNode<'a>>>,
    pub url2: Option<flatbuffers::WIPOffset<StringNode<'a>>>,
    pub url3: Option<flatbuffers::WIPOffset<StringNode<'a>>>,
}
impl<'a> Default for NodesDataArgs<'a> {
    #[inline]
    fn default() -> Self {
        NodesDataArgs {
            url1: None, // required field
            url2: None, // required field
            url3: None, // required field
        }
    }
}
pub struct NodesDataBuilder<'a: 'b, 'b> {
  fbb_: &'b mut flatbuffers::FlatBufferBuilder<'a>,
  start_: flatbuffers::WIPOffset<flatbuffers::TableUnfinishedWIPOffset>,
}
impl<'a: 'b, 'b> NodesDataBuilder<'a, 'b> {
  #[inline]
  pub fn add_url1(&mut self, url1: flatbuffers::WIPOffset<StringNode<'b >>) {
    self.fbb_.push_slot_always::<flatbuffers::WIPOffset<StringNode>>(NodesData::VT_URL1, url1);
  }
  #[inline]
  pub fn add_url2(&mut self, url2: flatbuffers::WIPOffset<StringNode<'b >>) {
    self.fbb_.push_slot_always::<flatbuffers::WIPOffset<StringNode>>(NodesData::VT_URL2, url2);
  }
  #[inline]
  pub fn add_url3(&mut self, url3: flatbuffers::WIPOffset<StringNode<'b >>) {
    self.fbb_.push_slot_always::<flatbuffers::WIPOffset<StringNode>>(NodesData::VT_URL3, url3);
  }
  #[inline]
  pub fn new(_fbb: &'b mut flatbuffers::FlatBufferBuilder<'a>) -> NodesDataBuilder<'a, 'b> {
    let start = _fbb.start_table();
    NodesDataBuilder {
      fbb_: _fbb,
      start_: start,
    }
  }
  #[inline]
  pub fn finish(self) -> flatbuffers::WIPOffset<NodesData<'a>> {
    let o = self.fbb_.end_table(self.start_);
    self.fbb_.required(o, NodesData::VT_URL1,"url1");
    self.fbb_.required(o, NodesData::VT_URL2,"url2");
    self.fbb_.required(o, NodesData::VT_URL3,"url3");
    flatbuffers::WIPOffset::new(o.value())
  }
}

impl std::fmt::Debug for NodesData<'_> {
  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
    let mut ds = f.debug_struct("NodesData");
      ds.field("url1", &self.url1());
      ds.field("url2", &self.url2());
      ds.field("url3", &self.url3());
      ds.finish()
  }
}
#[inline]
#[deprecated(since="2.0.0", note="Deprecated in favor of `root_as...` methods.")]
pub fn get_root_as_nodes_data<'a>(buf: &'a [u8]) -> NodesData<'a> {
  unsafe { flatbuffers::root_unchecked::<NodesData<'a>>(buf) }
}

#[inline]
#[deprecated(since="2.0.0", note="Deprecated in favor of `root_as...` methods.")]
pub fn get_size_prefixed_root_as_nodes_data<'a>(buf: &'a [u8]) -> NodesData<'a> {
  unsafe { flatbuffers::size_prefixed_root_unchecked::<NodesData<'a>>(buf) }
}

#[inline]
/// Verifies that a buffer of bytes contains a `NodesData`
/// and returns it.
/// Note that verification is still experimental and may not
/// catch every error, or be maximally performant. For the
/// previous, unchecked, behavior use
/// `root_as_nodes_data_unchecked`.
pub fn root_as_nodes_data(buf: &[u8]) -> Result<NodesData, flatbuffers::InvalidFlatbuffer> {
  flatbuffers::root::<NodesData>(buf)
}
#[inline]
/// Verifies that a buffer of bytes contains a size prefixed
/// `NodesData` and returns it.
/// Note that verification is still experimental and may not
/// catch every error, or be maximally performant. For the
/// previous, unchecked, behavior use
/// `size_prefixed_root_as_nodes_data_unchecked`.
pub fn size_prefixed_root_as_nodes_data(buf: &[u8]) -> Result<NodesData, flatbuffers::InvalidFlatbuffer> {
  flatbuffers::size_prefixed_root::<NodesData>(buf)
}
#[inline]
/// Verifies, with the given options, that a buffer of bytes
/// contains a `NodesData` and returns it.
/// Note that verification is still experimental and may not
/// catch every error, or be maximally performant. For the
/// previous, unchecked, behavior use
/// `root_as_nodes_data_unchecked`.
pub fn root_as_nodes_data_with_opts<'b, 'o>(
  opts: &'o flatbuffers::VerifierOptions,
  buf: &'b [u8],
) -> Result<NodesData<'b>, flatbuffers::InvalidFlatbuffer> {
  flatbuffers::root_with_opts::<NodesData<'b>>(opts, buf)
}
#[inline]
/// Verifies, with the given verifier options, that a buffer of
/// bytes contains a size prefixed `NodesData` and returns
/// it. Note that verification is still experimental and may not
/// catch every error, or be maximally performant. For the
/// previous, unchecked, behavior use
/// `root_as_nodes_data_unchecked`.
pub fn size_prefixed_root_as_nodes_data_with_opts<'b, 'o>(
  opts: &'o flatbuffers::VerifierOptions,
  buf: &'b [u8],
) -> Result<NodesData<'b>, flatbuffers::InvalidFlatbuffer> {
  flatbuffers::size_prefixed_root_with_opts::<NodesData<'b>>(opts, buf)
}
#[inline]
/// Assumes, without verification, that a buffer of bytes contains a NodesData and returns it.
/// # Safety
/// Callers must trust the given bytes do indeed contain a valid `NodesData`.
pub unsafe fn root_as_nodes_data_unchecked(buf: &[u8]) -> NodesData {
  flatbuffers::root_unchecked::<NodesData>(buf)
}
#[inline]
/// Assumes, without verification, that a buffer of bytes contains a size prefixed NodesData and returns it.
/// # Safety
/// Callers must trust the given bytes do indeed contain a valid size prefixed `NodesData`.
pub unsafe fn size_prefixed_root_as_nodes_data_unchecked(buf: &[u8]) -> NodesData {
  flatbuffers::size_prefixed_root_unchecked::<NodesData>(buf)
}
#[inline]
pub fn finish_nodes_data_buffer<'a, 'b>(
    fbb: &'b mut flatbuffers::FlatBufferBuilder<'a>,
    root: flatbuffers::WIPOffset<NodesData<'a>>) {
  fbb.finish(root, None);
}

#[inline]
pub fn finish_size_prefixed_nodes_data_buffer<'a, 'b>(fbb: &'b mut flatbuffers::FlatBufferBuilder<'a>, root: flatbuffers::WIPOffset<NodesData<'a>>) {
  fbb.finish_size_prefixed(root, None);
}
}  // pub mod node
}  // pub mod fb
}  // pub mod project
}  // pub mod company
}  // pub mod com

但问题是“即使 getter 代码不是由 flatc Rust 插件生成的，它在一般情况下是否可行？”。如果遵循应该可行的数据库概念。

PPS。使用 flatc "2.0.0"，使用 flatbuffers "2.0.0" crate。

Answer 1

不，你不能。 FlatBuffer 字段在内存中不一定是连续的，它们可能都有不同的类型，因此无法迭代它们。

虽然这可能可以通过足够的技巧（访问者？）来实现，但没有太多意义，尤其是在以效率为导向的系统中。

就像您自己已经说过的那样，在这种情况下您确实希望使用 [StringNode]。

我可以使用 FlatBuffers 遍历所有 table 项吗？

Can I iterate over all the table items with FlatBuffers?

rust

flatbuffers