使用 pyo3 返回文档对象向量时出错

Question

将文档对象的向量从 rust 返回到 python 失败。

我在 Rust 中有一个结构和方法实现，如下所示。

use mongodb::{
    bson::{Bson, Document},
    error::Error,
    sync::Client,
};
use pyo3::prelude::*;

#[pyclass]
pub struct SampleStruct{
    docs: Vec<Document>,
}

#[pymethods]
impl SampleStruct{
    #[new]
    pub fn new() -> Self {...}

    pub fn a_method(&self, some_string: &str) -> Vec<&Document> {...}
}

以上失败并显示以下消息

error[E0277]: the trait bound `std::vec::Vec<&bson::document::Document>: pyo3::callback::IntoPyCallbackOutput<_>` is not satisfied
   --> src/fail_demo.rs:55:1
    |
55  | #[pymethods]
    | ^^^^^^^^^^^^ the trait `pyo3::callback::IntoPyCallbackOutput<_>` is not implemented for `std::vec::Vec<&bson::document::Document>`
    | 
   ::: /home/demo/.cargo/registry/src/github.com-1ecc6299db9ec823/pyo3-0.11.1/src/callback.rs:169:8
    |
169 |     T: IntoPyCallbackOutput<U>,
    |        ----------------------- required by this bound in `pyo3::callback::convert`
    |
    = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)

Answer 1

最简单的方法是将 BSON 序列化为

bytes

，然后使用您选择的 BSON 库在 Python 中对其进行解码：

#[pyfunction]
fn bson_document<'py>(py: Python<'py>, key: &str, value: i32) -> PyResult<Bound<'py, PyBytes>> {
    let document = doc! {
        key: value,
        "otherKey": "otherValue",
    };
    let bytes = bson::to_vec(&document).map_err(|err| PyValueError::new_err(err.to_string()))?;
    Ok(PyBytes::new_bound(py, &bytes))
}

然后在 Python 中，例如使用

pymongo

:

import bson

doc = bson_document("myKey", -123)
print(bson.decode(doc))