Think\Db\Query::with PHP Method

    public function with($with)
    {
        if (empty($with)) {
            return $this;
        }
        if (is_string($with)) {
            $with = explode(',', $with);
        }
        $i = 0;
        $currentModel = $this->model;
        /** @var Model $class */
        $class = new $currentModel();
        foreach ($with as $key => $relation) {
            $closure = false;
            if ($relation instanceof \Closure) {
                // 支持闭包查询过滤关联条件
                $closure = $relation;
                $relation = $key;
                $with[$key] = $key;
            } elseif (is_string($relation) && strpos($relation, '.')) {
                $with[$key] = $relation;
                list($relation, $subRelation) = explode('.', $relation, 2);
            }
            /** @var Relation $model */
            $model = $class->{$relation}();
            $info = $model->getRelationInfo();
            if (in_array($info['type'], [Relation::HAS_ONE, Relation::BELONGS_TO])) {
                if (0 == $i) {
                    $name = Loader::parseName(basename(str_replace('\\', '/', $currentModel)));
                    $table = $this->getTable();
                    $alias = isset($info['alias'][$name]) ? $info['alias'][$name] : $name;
                    $this->table([$table => $alias]);
                    if (isset($this->options['field'])) {
                        $field = $this->options['field'];
                        unset($this->options['field']);
                    } else {
                        $field = true;
                    }
                    $this->field($field, false, $table, $alias);
                }
                // 预载入封装
                $joinTable = $model->getTable();
                $joinName = Loader::parseName(basename(str_replace('\\', '/', $info['model'])));
                $joinAlias = isset($info['alias'][$joinName]) ? $info['alias'][$joinName] : $relation;
                $this->via($joinAlias);
                if (Relation::HAS_ONE == $info['type']) {
                    $this->join($joinTable . ' ' . $joinAlias, $alias . '.' . $info['localKey'] . '=' . $joinAlias . '.' . $info['foreignKey'], $info['joinType']);
                } else {
                    $this->join($joinTable . ' ' . $joinAlias, $alias . '.' . $info['foreignKey'] . '=' . $joinAlias . '.' . $info['localKey'], $info['joinType']);
                }
                if ($closure) {
                    // 执行闭包查询
                    call_user_func_array($closure, [&$this]);
                    //指定获取关联的字段
                    //需要在 回调中 调方法 withField 方法，如
                    // $query->where(['id'=>1])->withField('id,name');
                    if (!empty($this->options['with_field'])) {
                        $field = $this->options['with_field'];
                        unset($this->options['with_field']);
                    }
                }
                $this->field($field, false, $joinTable, $joinAlias, $relation . '__');
                $i++;
            } elseif ($closure) {
                $with[$key] = $closure;
            }
        }
        $this->via();
        $this->options['with'] = $with;
        return $this;
    }