diesel_derives/
associations.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
use proc_macro2::{Span, TokenStream};
use quote::quote;
use syn::fold::Fold;
use syn::parse_quote;
use syn::{DeriveInput, Ident, Lifetime, Result};

use crate::model::Model;
use crate::parsers::BelongsTo;
use crate::util::{camel_to_snake, wrap_in_dummy_mod};

pub fn derive(item: DeriveInput) -> Result<TokenStream> {
    let model = Model::from_item(&item, false, false)?;

    if model.belongs_to.is_empty() {
        return Err(syn::Error::new(
            proc_macro2::Span::call_site(),
            "At least one `belongs_to` is needed for deriving `Associations` on a structure.",
        ));
    }

    let tokens = model
        .belongs_to
        .iter()
        .map(|assoc| derive_belongs_to(&item, &model, assoc))
        .collect::<Result<Vec<_>>>()?;

    Ok(wrap_in_dummy_mod(quote!(#(#tokens)*)))
}

fn derive_belongs_to(item: &DeriveInput, model: &Model, assoc: &BelongsTo) -> Result<TokenStream> {
    let (_, ty_generics, _) = item.generics.split_for_impl();

    let struct_name = &item.ident;
    let table_name = &model.table_names()[0];

    let foreign_key = &foreign_key(assoc);

    let foreign_key_field = model.find_column(foreign_key)?;
    let foreign_key_name = &foreign_key_field.name;
    let foreign_key_ty = &foreign_key_field.ty;

    let mut generics = item.generics.clone();

    let parent_struct = ReplacePathLifetimes::new(|i, span| {
        let letter = char::from(b'b' + i as u8);
        let lifetime = Lifetime::new(&format!("'__{letter}"), span);
        generics.params.push(parse_quote!(#lifetime));
        lifetime
    })
    .fold_type_path(assoc.parent.clone());

    generics.params.push(parse_quote!(__FK));
    {
        let where_clause = generics.where_clause.get_or_insert(parse_quote!(where));
        where_clause
            .predicates
            .push(parse_quote!(__FK: std::hash::Hash + std::cmp::Eq));
        where_clause.predicates.push(
                parse_quote!(for<'__a> &'__a #foreign_key_ty: std::convert::Into<::std::option::Option<&'__a __FK>>),
            );
        where_clause.predicates.push(
                parse_quote!(for<'__a> &'__a #parent_struct: diesel::associations::Identifiable<Id = &'__a __FK>),
            );
    }

    let foreign_key_expr = quote!(std::convert::Into::into(&self.#foreign_key_name));
    let foreign_key_ty = quote!(__FK);

    let (impl_generics, _, where_clause) = generics.split_for_impl();

    Ok(quote! {
        impl #impl_generics diesel::associations::BelongsTo<#parent_struct>
            for #struct_name #ty_generics
        #where_clause
        {
            type ForeignKey = #foreign_key_ty;
            type ForeignKeyColumn = #table_name::#foreign_key;

            fn foreign_key(&self) -> std::option::Option<&Self::ForeignKey> {
                #foreign_key_expr
            }

            fn foreign_key_column() -> Self::ForeignKeyColumn {
                #table_name::#foreign_key
            }
        }

        impl #impl_generics diesel::associations::BelongsTo<&'_ #parent_struct>
            for #struct_name #ty_generics
        #where_clause
        {
            type ForeignKey = #foreign_key_ty;
            type ForeignKeyColumn = #table_name::#foreign_key;

            fn foreign_key(&self) -> std::option::Option<&Self::ForeignKey> {
                #foreign_key_expr
            }

            fn foreign_key_column() -> Self::ForeignKeyColumn {
                #table_name::#foreign_key
            }
        }
    })
}

fn foreign_key(assoc: &BelongsTo) -> Ident {
    let ident = &assoc
        .parent
        .path
        .segments
        .last()
        .expect("paths always have at least one segment")
        .ident;

    assoc
        .foreign_key
        .clone()
        .unwrap_or_else(|| infer_foreign_key(ident))
}

fn infer_foreign_key(name: &Ident) -> Ident {
    let snake_case = camel_to_snake(&name.to_string());
    Ident::new(&format!("{snake_case}_id"), name.span())
}

struct ReplacePathLifetimes<F> {
    count: usize,
    f: F,
}

impl<F> ReplacePathLifetimes<F> {
    fn new(f: F) -> Self {
        Self { count: 0, f }
    }
}

impl<F> Fold for ReplacePathLifetimes<F>
where
    F: FnMut(usize, Span) -> Lifetime,
{
    fn fold_lifetime(&mut self, mut lt: Lifetime) -> Lifetime {
        if lt.ident == "_" {
            lt = (self.f)(self.count, lt.span());
            self.count += 1;
        }
        lt
    }
}