Replace strings with "null" value as real null values rusqlite

Question

I need to convert strings that have the value null to actual null values in a SQLite DB using rusqlite. I'm not in control of these string values. I've found the Null struct, but I'm not sure how to concisely pass it as a parameter, but then use the string value when it's not null.

sqlite.execute(
    "INSERT INTO people (name) VALUES (?1)",
    params![
        if person.name == "null" { &Null } else { person.name }
    ],
).unwrap();

But I get the error

`if` and `else` have incompatible types

expected `&rusqlite::types::Null`, found struct `std::string::String`rustc(E0308)

I could do something like this, but there has to be a better way.

if person.name == "null" {
    sqlite.execute(
        "INSERT INTO people (name) VALUES (?1)",
        params![
            &Null
        ],
    ).unwrap();
} else {
    sqlite.execute(
        "INSERT INTO people (name) VALUES (?1)",
        params![
            person.name
        ],
    ).unwrap();
}

I can only imagine how quickly something like this could get out of hand with multiple values in a more realistic setting. Is there some universal type I can covert the string type and the Null struct to? I could also make a SQL query to replace all these values once I'm done inserting, but I'd much rather do it right the first time around.

Answer 1

I'm not familiar with rusqlite, but in general, the tool for “might be null” in Rust is Option, and taking a look at rusqlite::ToSql confirms that there is a

impl<T: ToSql> ToSql for Option<T>

which does what you want. (It's undocumented, unfortunately, but following the “[src]” link shows its implementation.) To use it:

if person.name == "null" { None } else { Some(person.name) }

Answer 2

In addition to what @KevinReid said, the params![] macro converts all values to &dyn ToSql. So, one way is to use dyn ToSql:

sqlite
        .execute(
            "INSERT INTO people (name) VALUES (?1)",
            params![
                if person.name == "null" { &Null as &dyn ToSql } else { &person.name },
            ],
        )
        .unwrap()