func (mc *_modelCache) getByFN(name string) (mi *modelInfo, ok bool) {
	mi, ok = mc.cacheByFN[name]
	return
}
get model info by field name
package orm
import (
	"sync"
)
const (
	od_CASCADE            = "cascade"
	od_SET_NULL           = "set_null"
	od_SET_DEFAULT        = "set_default"
	od_DO_NOTHING         = "do_nothing"
	defaultStructTagName  = "orm"
	defaultStructTagDelim = ";"
)
var (
	modelCache = &_modelCache{
		cache:     make(map[string]*modelInfo),
		cacheByFN: make(map[string]*modelInfo),
	}
	supportTag = map[string]int{
		"-":            1,
		"null":         1,
		"index":        1,
		"unique":       1,
		"pk":           1,
		"auto":         1,
		"auto_now":     1,
		"auto_now_add": 1,
		"size":         2,
		"column":       2,
		"default":      2,
		"rel":          2,
		"reverse":      2,
		"rel_table":    2,
		"rel_through":  2,
		"digits":       2,
		"decimals":     2,
		"on_delete":    2,
		"type":         2,
	}
)
type _modelCache struct {
	sync.RWMutex
	orders    []string
	cache     map[string]*modelInfo
	cacheByFN map[string]*modelInfo
	done      bool
}
func (mc *_modelCache) all() map[string]*modelInfo {
	m := make(map[string]*modelInfo, len(mc.cache))
	for k, v := range mc.cache {
		m[k] = v
	}
	return m
}
func (mc *_modelCache) allOrdered() []*modelInfo {
	m := make([]*modelInfo, 0, len(mc.orders))
	for _, table := range mc.orders {
		m = append(m, mc.cache[table])
	}
	return m
}
func (mc *_modelCache) get(table string) (mi *modelInfo, ok bool) {
	mi, ok = mc.cache[table]
	return
}