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64 lines
2.4 KiB
Rust
64 lines
2.4 KiB
Rust
/// `macro_rules_attribute::derive(WithoutId!)` generates a variant of the struct with
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/// `WithoutId` added to the name and no `id` field.
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///
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/// This is useful for making less redundant selections of multiple joined tables.
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/// For example, selecting both `comment::post_id` and `post::id` is redundant if they
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/// have the same value. In this case, the selection of `post::id` can be avoided by selecting
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/// `PostWithoutId::as_select()` instead of `post::all_columns`.
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///
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/// This macro generates an `into_full` method, which converts to the sturct with `id`.
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/// For example, `PostWithoutId` would have this:
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///
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/// `pub fn into_full(self, id: PostId) -> Post`
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///
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/// The `id` value can come from a column in another table, like `comment::post_id`.
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///
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/// The generated struct implements `Selectable` and `Queryable`.
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macro_rules! WithoutId {
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(
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#[diesel(table_name = $table_name:ident)]
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$(#[$_struct_meta:meta])*
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$vis:vis struct $struct_name:ident {
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$(#[$_id_meta:meta])*
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$_id_vis:vis id: $id_type:ty,
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$(
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$(#[$_field_meta:meta])*
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$field_vis:vis $field_name:ident : $field_type:ty,
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)*
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}
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) => {
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::paste::paste! {
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#[derive(::diesel::Queryable, ::diesel::Selectable)]
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#[diesel(table_name = $table_name)]
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$vis struct [<$struct_name WithoutId>] {
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$(
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// Field attributes are not kept because either they are for other
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// derive macros, or they are `#[cfg(...)]` which is evaluated before
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// macro expansion.
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$field_vis $field_name : $field_type,
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)*
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}
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impl [<$struct_name WithoutId>] {
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pub fn into_full(self, id: $id_type) -> $struct_name {
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$struct_name {
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$($field_name : self.$field_name,)*
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id,
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}
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}
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}
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}
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};
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// Keep on removing the first attribute until `diesel(table_name = ...)` becomes
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// the first, which will cause the first pattern to be matched.
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(#[$_meta:meta] $($remaining:tt)*) => {
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$($remaining)*
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};
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// This pattern is matched when there's no attributes.
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($_vis:vis struct $($_tt:tt)*) => {
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::std::compile_error!("`#[diesel(table_name = ...)]` is missing");
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};
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}
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