mongo_orm_macro/
lib.rs

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use proc_macro::TokenStream;
use quote::quote;
use syn::{parse_macro_input, Data, DeriveInput, Fields};

#[proc_macro_derive(mongo_doc, attributes(foreign_key))]
pub fn mongo_entity_derive(input: TokenStream) -> TokenStream {
    let input = parse_macro_input!(input as DeriveInput);

    // Extract the struct name
    let name = input.ident;

    // Extract the fields from the struct
    let data = match input.data {
        Data::Struct(data) => data,
        _ => panic!("MongoEntity can only be derived for structs"),
    };

    let mut to_doc_fields = Vec::new();
    let mut from_doc_fields = Vec::new();

    if let Fields::Named(fields) = data.fields {
        for field in fields.named {
            let field_name = field.ident.clone().unwrap();
            let ty = field.ty.clone(); // Use the type of the field
            let is_foreign_key = field
                .attrs
                .iter()
                .any(|attr| attr.path().is_ident("foreign_key"));

            if field_name == "id" {
                // Special handling for `id` field
                to_doc_fields.push(if let syn::Type::Path(type_path) = &ty {
                    let type_string = quote!(#type_path).to_string();

                    if type_string.contains("Option") {
                        // If the type is Option<String> or Option<ObjectId>
                        quote! {
                            if let Some(value) = &self.#field_name {
                                if let Ok(object_id) = mongo_orm::bson::oid::ObjectId::parse_str(value) {
                                    doc.insert("_id", object_id);
                                } else {
                                    doc.insert("_id", value.clone());
                                }
                            } else {
                                doc.insert("_id", mongo_orm::bson::oid::ObjectId::new());
                            }
                        }
                    } else if type_string.contains("String") {
                        // If the type is String
                        quote! {
                            if let Ok(object_id) = mongo_orm::bson::oid::ObjectId::parse_str(&self.#field_name) {
                                doc.insert("_id", object_id);
                            } else {
                                doc.insert("_id", self.#field_name.clone());
                            }
                       }
                    } else {
                        // For other types, directly store the value
                        quote! {
                            doc.insert("_id", mongo_orm::bson::to_bson(&self.#field_name).unwrap());
                        }
                    }
                } else {
                    panic!("Unsupported type for `id` field");
                });

                // Generate logic for deserialization based on the type of `id`
                from_doc_fields.push(if let syn::Type::Path(type_path) = &ty {
                    let type_string = quote!(#type_path).to_string();

                    if type_string.contains("Option") {
                        // If the type is Option<String> or Option<ObjectId>
                        quote! {
                            #field_name: match doc.get("_id") {
                                Some(mongo_orm::bson::Bson::ObjectId(oid)) => Some(oid.to_hex()),
                                Some(mongo_orm::bson::Bson::String(s)) => Some(s.clone()),
                                _ => None,
                            },
                        }
                    } else if type_string.contains("String") {
                        // If the type is String
                        quote! {
                            #field_name: match doc.get("_id") {
                                Some(mongo_orm::bson::Bson::ObjectId(oid)) => oid.to_hex(),
                                Some(mongo_orm::bson::Bson::String(s)) => s.clone(),
                                _ => panic!("Missing or invalid _id field for {}", stringify!(#field_name)),
                            },
                        }
                    } else {
                        // Any other type is directly deserialized
                        quote! {
                            #field_name: mongo_orm::bson::from_bson(doc.remove("_id").expect()).unwrap(),
                        }
                    }
                } else {
                    panic!("Unsupported type for `id` field");
                });
            } else if is_foreign_key {
                to_doc_fields.push(if let syn::Type::Path(type_path) = &ty {
                    let type_string = quote!(#type_path).to_string();

                    if type_string.contains("Option") {
                        // Handle Option<String> or Option<ObjectId>
                        quote! {
                             if let Some(value) = &self.#field_name {
                                if let Ok(object_id) = mongo_orm::bson::oid::ObjectId::parse_str(value) {
                                    doc.insert(stringify!(#field_name), object_id);
                                } else {
                                    doc.insert(stringify!(#field_name), value.clone());
                                }
                            }
                        }
                    } else if type_string.contains("String") {
                        // If the type is String
                        quote! {
                            if let Ok(object_id) = mongo_orm::bson::oid::ObjectId::parse_str(&self.#field_name) {
                                doc.insert(stringify!(#field_name), object_id);
                            }
                            else {
                             doc.insert(stringify!(#field_name), self.#field_name.clone());
                            }
                        }
                    } else if type_string.contains("ObjectId") {
                        // If the type is ObjectId
                        quote! {
                            doc.insert(stringify!(#field_name), self.#field_name.clone());
                        }
                    } else {
                        panic!("Unsupported type for `foreign_key` field: {}", stringify!(#field_name));
                    }
                } else {
                    panic!("Unsupported type for `foreign_key` field: {}", stringify!(#field_name));
                });
                from_doc_fields.push(if let syn::Type::Path(type_path) = &ty {
                    let type_string = quote!(#type_path).to_string();

                    if type_string.contains("Option") {
                        quote! {
                            #field_name: match doc.get(stringify!(#field_name)) {
                                Some(mongo_orm::bson::Bson::ObjectId(oid)) => Some(oid.to_hex()),
                                Some(mongo_orm::bson::Bson::String(s)) => Some(s.clone()),
                                _ => None,
                            },
                        }
                    }else if type_string.contains("String") {
                        // If the type is String
                        quote! {
                             #field_name: match doc.get(stringify!(#field_name)) {
                                 Some(mongo_orm::bson::Bson::ObjectId(oid)) => oid.to_hex(),
                                 Some(mongo_orm::bson::Bson::String(s)) => s.clone(),
                                 _ => panic!("Invalid or missing foreign key: {}", stringify!(#field_name)),
                             },
                        }
                    } else if type_string.contains("ObjectId") {
                        // If the type is ObjectId
                        quote! {
                            #field_name: match doc.get(stringify!(#field_name)) {
                                Some(mongo_orm::bson::Bson::ObjectId(oid)) => oid.clone(),
                                _ => panic!("Invalid or missing foreign key: {}", stringify!(#field_name)),
                            },
                        }
                    } else {
                        panic!("Unsupported type for `foreign_key` field: {}", stringify!(#field_name));
                    }
                } else {
                    panic!("Unsupported type for `foreign_key` field: {}", stringify!(#field_name));
                });
            } else {
                // Handle regular fields
                to_doc_fields.push(quote! {
                    doc.insert(stringify!(#field_name), mongo_orm::bson::to_bson(&self.#field_name).unwrap());
                });

                let field_expr = if let syn::Type::Path(type_path) = &ty {
                    let type_string = quote!(#type_path).to_string();
                    if type_string.contains("Option") {
                        // For Option types, map the removal to an Option conversion.
                        quote! {
                            doc.remove(stringify!(#field_name))
                                .map(|bson| mongo_orm::bson::from_bson(bson).unwrap())
                        }
                    } else {
                        // For non-Option types, expect the field to be present.
                        quote! {
                            mongo_orm::bson::from_bson(doc.remove(stringify!(#field_name)).expect("Field missing")).unwrap()
                        }
                    }
                } else {
                    // Default to required field
                    quote! {
                        mongo_orm::bson::from_bson(doc.remove(stringify!(#field_name)).expect("Field missing")).unwrap()
                    }
                };

                from_doc_fields.push(quote! {
                    #field_name: #field_expr,
                });
            }
        }
    }

    // Generate the implementation
    let expanded = quote! {
        impl mongo_orm::entity::MongoEntity for #name {
            fn to_document(&self) -> mongo_orm::bson::Document {
                let mut doc = mongo_orm::bson::Document::new();
                #(#to_doc_fields)*
                doc
            }

            fn from_document(mut doc: mongo_orm::bson::Document) -> Self {
                Self {
                    #(#from_doc_fields)*
                }
            }
        }
    };

    // Convert the implementation into a token stream and return
    TokenStream::from(expanded)
}