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"APEX" is a set of stored procedures that is installed in the database. "ORDS" is a Java application that is installed on Tomcat and talks to APEX in the database. I wrote a guide on this a couple of years ago. Doesn't sound like you'd need the high availability or header authentication parts, but the initial setup is largely the same. It might add to your understanding, anyway. See here:

• https://pmdba.files.wordpress.com/2019/09/ha-oracle-ords-apex-with-http-header-authentication.pdf

Mapping a Timestamptz field to a DateTime is not supported by diesel itself, as it only provides the corresponding impl for DateTime. You can work this around by using the #[diesel(deserialize_as = "…")] attribute on the corresponding field and providing your own deserialization wrapper:

This is because the threads spawned inside the loop need to take ownership of pool, as each thread could run for longer than main. Referencing pool owned by main from inside a thread could lead to referencing a value that has already been destroyed if main exits while the threads are still running.

Taking ownership of pool requires you to clone it each time the loop executes, so each thread has its own copy.

Internally, a Pool is an std::sync::Arc and the Clone implementation simply clones the Arc. That is, each clone of Pool is just an incremented reference count. As the threads are created, the reference count is increased. When the threads finish, they decrement the reference count by dropping their Pool, destroying the underlying connection when the reference count reaches zero.

The r2d2-mongodb is outdated and no longer supported, the r2d2 crate marks it as:

deprecated: official driver handles pooling internally

So I recommend you don't use it. You should be able to use a mongodb::Client or mongodb::Database instead of a Pool.

The reason for the error is the r2d2-mongodb uses an older version of mongodb (0.3) and therefore an older version of bson (0.13) that is incompatible with the version of bson you're using (1.1.0). You'll probably have similar compatibility issues with the mongodb crate itself as well. You can fix it by lowering your dependencies:

You need to include serde feature in chrono in your Cargo.toml:

You should use List in second case as well - ForEach is just a dynamic group which does not have selection feature:

Your comparing the id as well as the email to themselves. What you want is to compare the database field's value to the value in your code.

For diesel, this typically means you need to import your schema, like so:

Thanks to some comments, I figured out a way that the Rust compiler accepts:

You are storing your data at each iteration in the same dataframe, rewriting it at each iteration, so you only have your last data (twice actually, because of df2.append(df2).

Here is a slightly modified version, storing each dataframe in df_list, and using pd.concat on this list to create df3: