diesel | Mini query engine used to power our various DSL frameworks

Try this. Your code was confusing in how it used the array a, but I think this is the gist. Really, you should have told us what you were trying to do here.

I think you just need to fix your current query:

Duplicates, yes. Because you did it partially wrong. Should have been

You need to commit the TextField (by pressing enter) first before calling saveVehicle.

If you instead to the following in your view model:

You can use cargo features to enable multiple optional dependencies.

Here is an example:

First of all: Always provide a complete minimal example of your problem. This includes the exact version of all used crates, all relevant imports to make your code actually producing this error message, the complete error message with all help and notice statements and in diesels case the generated schema file.

To answer your question: You miss two call to .single_value() which is required to convert a query into a subquery that could be used as expression. Both subqueries return a Nullable therefore it is required that opening_balance as a matching type.

For the sake of completeness see the working code below

I can't say exactly why empty DataFrame with columns fails to append a line. But if you append the same line to the regular empty DataFrame, it works fine:

Errors like these usually mean that diesel could not resolve your trait bounds, due to not being restrictive enough.

Diesel generic programming is usually a bit more complex, but here's a few tips to help you the next time you get this error:

• Whenever you use want to use a specific method like find, you have to make sure you also check for the same bounds!
• Prefer to build specific re-usable pieces of functions that will allow you to get what you want
• Every time you call a diesel method you are 'wrapping' a new statement, this new statement has to be bound or you will get weird error messages like in your question.
• The result of these methods usually have a shorthand like Find or Limit in code below
• As you can see on line 27, we have to nest Limit<..>>, for every new method you call in the query chain, you will need to specify this.

If I understand correctly, you're looking for a way to keep your rust entities and db schema in sync, without having to write any SQL (which is basically what a regular orm like EFCore or GORM would provide).

If that's what you need, I'm afraid diesel won't do what you're looking for. There is this library which looks nice https://github.com/rust-db/barrel, and it provides a way for you to write your migrations in Rust instead of SQL, a bit like EFCore.

diesel also provides the embed_migrations! macro, which you can use in order to automatically run migrations without using the cli.

However, while all these tools will sort of help you out in automating your db migrations, you're still going to have to write them manually.