feat: one-to-many relation helper

Allow one to specify that a field of a model is a foreign key.
It will generate a bunch of helper methods to query related entities
from one entity.

lib/sqlxgentools_cli/src/generators/repositories/relations.rs

@@ -0,0 +1,71 @@
+use proc_macro2::TokenStream;
+use quote::{format_ident, quote};
+
+use crate::models::{Field, FieldForeignMode, Model};
+
+pub fn gen_get_many_by_related_entity_method(model: &Model, foreign_key_field: &Field) -> TokenStream {
+    let resource_ident = format_ident!("{}", &model.name);
+
+    let foreign_ref_params = match &foreign_key_field.foreign_mode {
+        FieldForeignMode::ForeignRef(params) => params,
+        FieldForeignMode::NotRef => {
+            panic!("Expected foreign key");
+        } 
+    };
+
+    let select_query = format!("SELECT * FROM {} WHERE {} = $1", model.table_name, foreign_key_field.name);
+
+    let func_name_ident = format_ident!("get_many_{}_by_{}", foreign_ref_params.reverse_relation_name, foreign_ref_params.target_resource_name);
+
+    quote! {
+        pub async fn #func_name_ident(&self, item_id: &str) -> Result<Vec<#resource_ident>, sqlx::Error> {
+            sqlx::query_as::<_, #resource_ident>(#select_query)
+                .bind(item_id)
+                .fetch_all(&self.db.0)
+                .await
+        }
+    }
+}
+
+pub fn gen_get_many_by_related_entities_method(all_models: &[Model], model: &Model, foreign_key_field: &Field) -> TokenStream {
+    let resource_ident = format_ident!("{}", &model.name);
+
+    let foreign_ref_params = match &foreign_key_field.foreign_mode {
+        FieldForeignMode::ForeignRef(params) => params,
+        FieldForeignMode::NotRef => {
+            panic!("Expected foreign key");
+        } 
+    };
+
+    let select_query = format!("SELECT * FROM {} WHERE {} IN ({{}})", model.table_name, foreign_key_field.name);
+
+    let target_resource = all_models.iter()
+        .find(|m| m.name.to_lowercase() == foreign_ref_params.target_resource_name.to_lowercase())
+        .expect("Could not find foreign ref target type associated resource");
+
+    let func_name_ident = format_ident!("get_many_{}_by_{}", foreign_ref_params.reverse_relation_name, target_resource.table_name);
+
+    quote! {
+        pub async fn #func_name_ident(&self, items_ids: Vec<String>) -> Result<Vec<#resource_ident>, sqlx::Error> {
+            if items_ids.is_empty() {
+                return Ok(vec![])
+            }
+            let placeholder_params: String = (1..=(items_ids.len()))
+                .map(|i| format!("${i}"))
+                .collect::<Vec<String>>()
+                .join(",");
+            let query_tmpl = format!(
+                #select_query,
+                placeholder_params
+            );
+            let mut query = sqlx::query_as::<_, #resource_ident>(&query_tmpl);
+            for id in items_ids {
+                query = query.bind(id)
+            }
+
+            query
+                .fetch_all(&self.db.0)
+                .await
+        }
+    }
+}