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added to_json function #4229

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merged 6 commits into from
Sep 4, 2024
Merged

added to_json function #4229

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a65e709
added to_json function
Sep 3, 2024
8970d56
fixed formatting
Sep 3, 2024
950bba4
fixed docs
Sep 3, 2024
c2135ae
addressed review
Sep 4, 2024
8089dff
Fix nullability of the `to_json` return type
weiznich Sep 4, 2024
df57cf5
Use a helper type to workaround new rust syntax
weiznich Sep 4, 2024
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44 changes: 44 additions & 0 deletions diesel/src/pg/expression/functions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1423,3 +1423,47 @@ define_sql_function! {
/// ```
fn array_upper<Arr: ArrayOrNullableArray + SingleValue>(array: Arr, dimension: Integer) -> Nullable<Integer>;
}

#[cfg(feature = "postgres_backend")]
define_sql_function! {
/// Converts any SQL value to json
///
/// # Example
///
/// ```rust
/// # include!("../../doctest_setup.rs");
/// #
/// # fn main() {
/// # run_test().unwrap();
/// # }
/// #
/// # fn run_test() -> QueryResult<()> {
/// # use diesel::dsl::to_json;
/// # use serde_json::{json, Value};
/// # use diesel::sql_types::{Integer, Array, Json, Text, Nullable};
/// # let connection = &mut establish_connection();
/// let result = diesel::select(to_json::<Integer, _>(1))
/// .get_result::<Value>(connection)?;
///
/// assert_eq!(json!(1), result);
///
/// let result = diesel::select(to_json::<Array<Text>, _>(vec!["abc", "xyz"]))
/// .get_result::<Value>(connection)?;
///
/// assert_eq!(json!(["abc", "xyz"]), result);
///
/// let result = diesel::select(to_json::<Array<Nullable<Text>>, _>(Vec::<String>::new()))
/// .get_result::<Value>(connection)?;
///
/// assert_eq!(json!([]), result);
///
/// let result = diesel::select(to_json::<Nullable<Text>, _>(None::<String>))
/// .get_result::<Value>(connection);
///
/// assert_eq!(result.unwrap_err().to_string(), "Unexpected null for non-null column");
///
/// # Ok(())
/// # }
/// ```
fn to_json<E: SingleValue>(e: E) -> Json;
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This function seems to return null if you pass in a null values. We want to have a doc test demonstrating that this is correctly propagated.

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ive changed the last test a bit, let me know if its okay

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No, that's not what I had in mind. My idea was to make the return type Nullable<Json> if the argument is nullable and Json for non-null arguments. As I did not know without a quick experiment how to do that I've pushed 8089dff to change it. (I needed to try it myself anyway).

To explain what's going on there:

  • The SqlType trait as a IsNull associated type that indicates whether the current type is nullable or not. We can access it as it's a super trait of SingleValue
  • The IsNull type implements MaybeNullableType<T> which wraps T into Nullable if the input type was nullable, otherwise it will just result in T.

By using that as return type we enforce that we return a non-nullable value for non-nullable inputs and nullable types otherwise, which allows us to correctly write the last test case.

}
5 changes: 5 additions & 0 deletions diesel/src/pg/expression/helper_types.rs
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Expand Up @@ -461,3 +461,8 @@ pub type array_positions<A, E> =
#[allow(non_camel_case_types)]
#[cfg(feature = "postgres_backend")]
pub type array_ndims<A> = super::functions::array_ndims<SqlTypeOf<A>, A>;

/// Return type of [`to_json(element)`](super::functions::to_json())
#[allow(non_camel_case_types)]
#[cfg(feature = "postgres_backend")]
pub type to_json<E> = super::functions::to_json<SqlTypeOf<E>, E>;
1 change: 1 addition & 0 deletions diesel_derives/tests/auto_type.rs
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Expand Up @@ -432,6 +432,7 @@ fn postgres_functions() -> _ {
array_position_with_subscript(pg_extras::array, pg_extras::id, pg_extras::id),
array_positions(pg_extras::array, pg_extras::id),
array_ndims(pg_extras::array),
to_json(pg_extras::id),
)
}

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