From f999240e106552c62eef70d29d1da93d95f76a5b Mon Sep 17 00:00:00 2001
From: Jinzhu <wosmvp@gmail.com>
Date: Thu, 14 May 2020 20:54:50 +0800
Subject: [PATCH] Define association API, add conds to when preloading

---
 association.go       | 54 +++++++++++++++++++++++++++++++++++++++++++-
 callbacks/preload.go | 10 ++++----
 2 files changed, 58 insertions(+), 6 deletions(-)

diff --git a/association.go b/association.go
index 14bc54b6..a9345255 100644
--- a/association.go
+++ b/association.go
@@ -1,9 +1,61 @@
 package gorm
 
+import (
+	"fmt"
+
+	"github.com/jinzhu/gorm/schema"
+)
+
 // Association Mode contains some helper methods to handle relationship things easily.
 type Association struct {
+	DB           *DB
+	Relationship *schema.Relationship
+	Error        error
 }
 
 func (db *DB) Association(column string) *Association {
-	return nil
+	association := &Association{DB: db}
+
+	if err := db.Statement.Parse(db.Statement.Model); err == nil {
+		association.Relationship = db.Statement.Schema.Relationships.Relations[column]
+
+		if association.Relationship == nil {
+			association.Error = fmt.Errorf("%w: %v", ErrUnsupportedRelation, column)
+		}
+	} else {
+		association.Error = err
+	}
+
+	return association
+}
+
+func (association *Association) Find(out interface{}, conds ...interface{}) error {
+	if association.Error == nil {
+		for _, ref := range association.Relationship.References {
+			if ref.OwnPrimaryKey {
+			}
+		}
+	}
+
+	return association.Error
+}
+
+func (association *Association) Append(values ...interface{}) error {
+	return association.Error
+}
+
+func (association *Association) Replace(values ...interface{}) error {
+	return association.Error
+}
+
+func (association *Association) Delete(values ...interface{}) error {
+	return association.Error
+}
+
+func (association *Association) Clear() error {
+	return association.Error
+}
+
+func (association *Association) Count() int {
+	return 0
 }
diff --git a/callbacks/preload.go b/callbacks/preload.go
index 8ab014f6..aaac31b5 100644
--- a/callbacks/preload.go
+++ b/callbacks/preload.go
@@ -84,7 +84,7 @@ func getIdentityFieldValuesMap(reflectValue reflect.Value, fields []*schema.Fiel
 	return dataResults, results
 }
 
-func preloadData(tx *gorm.DB, resultSchema *schema.Schema, foreignKeys []string, foreignValues [][]interface{}) reflect.Value {
+func preloadData(tx *gorm.DB, resultSchema *schema.Schema, foreignKeys []string, foreignValues [][]interface{}, conds []interface{}) reflect.Value {
 	slice := reflect.MakeSlice(reflect.SliceOf(resultSchema.ModelType), 0, 0)
 	results := reflect.New(slice.Type())
 	results.Elem().Set(slice)
@@ -94,12 +94,12 @@ func preloadData(tx *gorm.DB, resultSchema *schema.Schema, foreignKeys []string,
 		for idx, r := range foreignValues {
 			queryValues[idx] = r[0]
 		}
-		tx.Where(clause.IN{Column: foreignKeys[0], Values: queryValues}).Find(results.Interface())
+		tx.Where(clause.IN{Column: foreignKeys[0], Values: queryValues}).Find(results.Interface(), conds...)
 	} else {
 		for idx, r := range foreignValues {
 			queryValues[idx] = r
 		}
-		tx.Where(clause.IN{Column: foreignKeys, Values: queryValues}).Find(results.Interface())
+		tx.Where(clause.IN{Column: foreignKeys, Values: queryValues}).Find(results.Interface(), conds...)
 	}
 
 	return results.Elem()
@@ -139,7 +139,7 @@ func preload(db *gorm.DB, rels []*schema.Relationship, conds []interface{}) {
 		}
 
 		joinIdentityMap, joinForeignValues := getIdentityFieldValuesMap(reflectValue, joinForeignFields)
-		joinResults := preloadData(tx, rel.JoinTable, joinForeignKeys, joinForeignValues)
+		joinResults := preloadData(tx, rel.JoinTable, joinForeignKeys, joinForeignValues, nil)
 
 		// convert join identity map to relation identity map
 		fieldValues := make([]reflect.Value, len(foreignFields))
@@ -177,7 +177,7 @@ func preload(db *gorm.DB, rels []*schema.Relationship, conds []interface{}) {
 		identityMap, foreignValues = getIdentityFieldValuesMap(reflectValue, foreignFields)
 	}
 
-	reflectResults := preloadData(tx, rel.FieldSchema, relForeignKeys, foreignValues)
+	reflectResults := preloadData(tx, rel.FieldSchema, relForeignKeys, foreignValues, conds)
 
 	fieldValues := make([]reflect.Value, len(foreignFields))
 	for i := 0; i < reflectResults.Len(); i++ {