A database connection problem in onethink

Onethink AdminArticlegetDocumentList () method; I directly pasted the code {code ...} {code ...} this link cannot be understood. Can someone explain it to me? & #039 ;__ DOCUMENT _ & #039 ;. strtoupper ($ modelName) represents another model. & #039 ;__... the Admin/Article/getDocumentList () method of onethink;
I directly pasted the code.

Protected function getDocumentList ($ cate_id = 0, $ model_id = null, $ position = null, $ field = true, $ group_id = null) {/* query condition initialization */$ map = array (); if (isset ($ _ GET ['title']) {$ map ['title'] = array ('like', '% '. (string) I ('title '). '%');} if (isset ($ _ GET ['status']) {$ map ['status'] = I ('status '); $ status = $ map ['status'];} else {$ status = null; $ map ['status'] = array ('in', '0, 1, 2 ');} if (isset ($ _ GET ['start']) {$ Map ['Update _ time'] [] = array ('egt', strtotime (I ('start ')));} if (isset ($ _ GET ['end']) {$ map ['Update _ time'] [] = array ('elt ', 24*60*60 + strtotime (I ('end');} if (isset ($ _ GET ['nickname']) {$ map ['uid'] = M ('member')-> where (array ('nickname' => I ('nickname '))) -> getField ('uid');} if (! Is_administrator (UID) {$ map ["uid"] = UID;} // construct list data $ Document = M ('document'); if ($ cate_id) {$ map ['category _ id'] = $ cate_id;} $ map ['pid '] = I ('pid', 0 ); if ($ map ['pid ']) {// The Sub-document list ignores the category unset ($ map ['category _ id']);} $ Document-> alias ('document'); if (! Is_null ($ model_id) {$ map ['model _ id'] = $ model_id; if (is_array ($ field) & array_diff ($ Document-> getDbFields (), $ field) {$ modelName = M ('model')-> getFieldById ($ model_id, 'name'); $ Document-> join ('_ DOCUMENT _'. strtoupper ($ modelName ). '__'. $ modelName. 'on document. id = '. $ modelName. '. id'); $ key = array_search ('id', $ field); if (false! ==$ Key) {unset ($ field [$ key]); $ field [] = 'document. id' ;}} if (! Is_null ($ position) {$ map [] = "position & {$ position }={ $ position}";} if (! Is_null ($ group_id) {$ map ['group _ id'] = $ group_id;} $ list = $ this-> lists ($ Document, $ map, 'level DESC, DOCUMENT. id DESC ', $ field); if ($ map ['pid']) {// obtain the superior Document $ article = $ Document-> field ('Id, title, type ')-> find ($ map ['pid']); $ this-> assign ('Article', $ article );} // check whether the specified category allows content to be published. $ allow_publish = get_category ($ cate_id, 'Allow _ publish '); $ this-> assign ('status', $ status ); $ this-> assign ('allow', $ allow_publish); $ this-> assign ('pid ', $ map ['pid']); $ this-> meta_title = 'document list'; return $ list ;}

Where

$Document->join('__DOCUMENT_'.strtoupper($modelName).'__ '.$modelName.' ON DOCUMENT.id='.$modelName.'.id');

This link cannot be understood. Can someone help me explain it? I know.'__DOCUMENT_'.strtoupper($modelName)Represents another model.'__ '.$modelName.'This is useless.

Reply content:

The Admin/Article/getDocumentList () method of onethink;
I directly pasted the code.

Protected function getDocumentList ($ cate_id = 0, $ model_id = null, $ position = null, $ field = true, $ group_id = null) {/* query condition initialization */$ map = array (); if (isset ($ _ GET ['title']) {$ map ['title'] = array ('like', '% '. (string) I ('title '). '%');} if (isset ($ _ GET ['status']) {$ map ['status'] = I ('status '); $ status = $ map ['status'];} else {$ status = null; $ map ['status'] = array ('in', '0, 1, 2 ');} if (isset ($ _ GET ['start']) {$ Map ['Update _ time'] [] = array ('egt', strtotime (I ('start ')));} if (isset ($ _ GET ['end']) {$ map ['Update _ time'] [] = array ('elt ', 24*60*60 + strtotime (I ('end');} if (isset ($ _ GET ['nickname']) {$ map ['uid'] = M ('member')-> where (array ('nickname' => I ('nickname '))) -> getField ('uid');} if (! Is_administrator (UID) {$ map ["uid"] = UID;} // construct list data $ Document = M ('document'); if ($ cate_id) {$ map ['category _ id'] = $ cate_id;} $ map ['pid '] = I ('pid', 0 ); if ($ map ['pid ']) {// The Sub-document list ignores the category unset ($ map ['category _ id']);} $ Document-> alias ('document'); if (! Is_null ($ model_id) {$ map ['model _ id'] = $ model_id; if (is_array ($ field) & array_diff ($ Document-> getDbFields (), $ field) {$ modelName = M ('model')-> getFieldById ($ model_id, 'name'); $ Document-> join ('_ DOCUMENT _'. strtoupper ($ modelName ). '__'. $ modelName. 'on document. id = '. $ modelName. '. id'); $ key = array_search ('id', $ field); if (false! ==$ Key) {unset ($ field [$ key]); $ field [] = 'document. id' ;}} if (! Is_null ($ position) {$ map [] = "position & {$ position }={ $ position}";} if (! Is_null ($ group_id) {$ map ['group _ id'] = $ group_id;} $ list = $ this-> lists ($ Document, $ map, 'level DESC, DOCUMENT. id DESC ', $ field); if ($ map ['pid']) {// obtain the superior Document $ article = $ Document-> field ('Id, title, type ')-> find ($ map ['pid']); $ this-> assign ('Article', $ article );} // check whether the specified category allows content to be published. $ allow_publish = get_category ($ cate_id, 'Allow _ publish '); $ this-> assign ('status', $ status ); $ this-> assign ('allow', $ allow_publish); $ this-> assign ('pid ', $ map ['pid']); $ this-> meta_title = 'document list'; return $ list ;}

Where

$Document->join('__DOCUMENT_'.strtoupper($modelName).'__ '.$modelName.' ON DOCUMENT.id='.$modelName.'.id');

This link cannot be understood. Can someone help me explain it? I know.'__DOCUMENT_'.strtoupper($modelName)Represents another model.'__ '.$modelName.'This is useless.

The alias is equivalent