Fix for #692

api.php

     						break;
     					case 'decimal':
     						if (strpos($value, '.') !== false) {
-    							list($whole, $decimals) = explode('.', $value, 2);
+    							list($whole, $decimals) = explode('.', ltrim($value, '-'), 2);
     						} else {
-    							list($whole, $decimals) = array($value, '');
+    							list($whole, $decimals) = array(ltrim($value, '-'), '');
     						}
     						if (strlen($whole) > 0 && !ctype_digit($whole)) {
     							return 'invalid decimal';

src/Tqdev/PhpCrudApi/Middleware/ValidationMiddleware.php

 						break;
 					case 'decimal':
 						if (strpos($value, '.') !== false) {
-							list($whole, $decimals) = explode('.', $value, 2);
+							list($whole, $decimals) = explode('.', ltrim($value, '-'), 2);
 						} else {
-							list($whole, $decimals) = array($value, '');
+							list($whole, $decimals) = array(ltrim($value, '-'), '');
 						}
 						if (strlen($whole) > 0 && !ctype_digit($whole)) {
 							return 'invalid decimal';

tests/functional/003_columns/015_update_types_table.log

 ===
 PUT /records/types/1
 
+{"decimal":"-1.23"}
+===
+200
+Content-Type: application/json; charset=utf-8
+Content-Length: 1
+
+1
+===
+PUT /records/types/1
+
+{"decimal":"1.23"}
+===
+200
+Content-Type: application/json; charset=utf-8
+Content-Length: 1
+
+1
+===
+PUT /records/types/1
+
 {"decimal":"12.23.34"}
 ===
 422