thinkphp Illegal data Object solution

thinkphp Illegal Data Objects
$data = $_post;
$data [' user_id '] = 1;
$data [' create_at '] = Date ("y-m-d h:i:s");
$data [' update_at '] = Date ("y-m-d h:i:s");
$data [' is_enable '] = 1;
$data [' is_visible '] = 1;
$categoryModel = new \admin\model\categorymodel ();
$footPosition = $categoryModel->getfootposition ();
$data [' position '] = intval ($footPosition) + 1;


Var_dump ($data);
$categoryModel->add ($data);
I started to think that the position type was wrong, but whether it was a string or an int, it was the same as reporting an illegal data object error. $data [' position '] = intval ($footPosition) + 1; This comment is no problem with inserting data. Help me.

Var_dump after the results are as follows, can not see what the problem ah.
Array (7) {["Category_name"]=> string (12) "Rumblings" ["user_id"]=> int (1) ["Create_at"]=> string (19) "2015-04-05 15 : 39:41 "[" Update_at "]=> string ()" 2015-04-05 15:39:41 "[" Is_enable "]=> int (1) [" is_visible "]=> int (1) [" Position "]=> int (2)}

The database field position, determined not to contain spaces, and the column names are consistent.

------to solve the idea----------------------
$footPosition = $categoryModel->getfootposition ();
And then print out $footPosition see what it is

In addition, the original error message should be given when an error occurs

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