Mismatched Types: Expected `RawDocumentBuf`, Found `Document`

Mismatched Types: Expected RawDocumentBuf, Found Document

When working with the MongoDB Rust driver, it's not uncommon to encounter errors related to type mismatches. In this article, we'll delve into a specific issue where the expected type is RawDocumentBuf, but the found type is Document. We'll explore the error message, identify the root cause, and provide a solution to resolve the issue.

Before we dive into the issue, let's take a look at the versions and environment used:

• Rust version: 1.78
• Operating system: Ubuntu
• MongoDB driver version: 3.2.1 (main branch)
• BSON driver version: 2.13.0 (main branch)

The issue arises when trying to compile the library, resulting in a mismatched types error. The error message is as follows:

error[E0308]: mismatched types
   --> /home/runner/.cargo/git/checkouts/mongo-rust-driver-b939e0128fabb835/f258c21/src/operation/bulk_write.rs:129:67
    |
129 | ...                   RunCommand::new(namespace.db.clone(), kill_cursors, None, None)?;
    |                       ---------------                       ^^^^^^^^^^^^ expected `RawDocumentBuf`, found `Document`
    |                       |
    |                       arguments to this function are incorrect
    |
note: associated function defined here
   --> /home/runner/.cargo/git/checkouts/mongo-rust-driver-b939e0128fabb835/f258c21/src/operation/run_command.rs:22:19
    |
22  |     pub(crate) fn new(
    |                   ^^^
23  |         db: String,
24  |         command: RawDocumentBuf,
    |         -----------------------

error[E0277]: the `?` operator can only be applied to values that implement `Try`
   --> /home/runner/.cargo/git/checkouts/mongo-rust-driver-b939e0128fabb835/f258c21/src/operation/bulk_write.rs:129:29
    |
129 | ...                   RunCommand::new(namespace.db.clone(), kill_cursors, None, None)?;
    |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the `?` operator cannot be applied to type `operation::run_command::RunCommand<'_>`
    |
    = help: the trait `Try` is not implemented for `operation::run_command::RunCommand<'_>`

The root cause of this issue lies in the RunCommand function, which expects a RawDocumentBuf as its second argument. However, the provided value is a Document, which is not compatible with the expected type.

To resolve this issue, we need to ensure that the RunCommand function receives a RawDocumentBuf as its second argument. We can achieve this by converting the Document to a RawDocumentBuf using the to_raw_document_buf method.

Here's the corrected code:

let command = Document::new(kill_cursors).to_raw_document_buf()?;
RunCommand::new(namespace.db.clone(), command, None None)?;

By making this change, we ensure that the RunCommand function receives a RawDocumentBuf as its second argument, resolving the type mismatch error.

In this article, we explored a specific issue related to type mismatches in the MongoDB Rust driver. We identified the root cause, which was a mismatch between the expected RawDocumentBuf and the found Document type. We provided a solution to resolve the issue by converting the Document to a RawDocumentBuf using the to_raw_document_buf method. By following this solution, developers can resolve similar type mismatch errors and ensure a smooth development experience with the MongoDB Rust driver.
Mismatched Types: Expected RawDocumentBuf, Found Document - Q&A

In our previous article, we explored a specific issue related to type mismatches in the MongoDB Rust driver. We identified the root cause, which was a mismatch between the expected RawDocumentBuf and the found Document type. In this article, we'll provide a Q&A section to help developers better understand the issue and its solution.

A: The expected type in the RunCommand function is RawDocumentBuf.

A: The found type in the RunCommand function is Document.

A: The type mismatch occurs because the RunCommand function expects a RawDocumentBuf as its second argument, but the provided value is a Document.

A: To resolve the type mismatch error, you can convert the Document to a RawDocumentBuf using the to_raw_document_buf method.

A: The to_raw_document_buf method is a method provided by the Document type that converts a Document to a RawDocumentBuf.

A: To use the to_raw_document_buf method, you can call it on a Document instance, like this:

let command = Document::new(kill_cursors).to_raw_document_buf()?;

A: The ? operator is used to propagate errors from the to_raw_document_buf method. If the method returns an error, the ? operator will return the error from the to_raw_document_buf method.

A: No, you can only use the to_raw_document_buf method with a Document instance that has a valid RawDocumentBuf representation.

A: The RunCommand function is commonly used to execute database commands, such as the killCursors command.

A: Yes, you can use the RunCommand function with other types of commands, as long as they have a valid RawDocumentBuf representation.

In this Q&A article, we provided answers to common questions related to the type mismatch issue in the MongoDB Rust driver. We hope that this article has helped developers better understand the issue and its solution, and has provided a useful resource for resolving similar type mismatch errors.