fix: json fields not parsed properly (#20866)

* fix: json fields not parsed properly

* fix: prevent stringifying twice

packages/core/admin/admin/src/components/FormInputs/Json.tsx

@@ -24,7 +24,9 @@ const JsonInput = forwardRef<JSONInputRef, InputProps>(
         <Field.Label action={labelAction}>{label}</Field.Label>
         <JSONInputImpl
           ref={composedRefs}
-          value={field.value}
+          value={
+            typeof field.value == 'object' ? JSON.stringify(field.value, null, 2) : field.value
+          }
           onChange={(json) => {
             // Default to null when the field is not required and there is no input value
             const value = required && !json.length ? null : json;

packages/core/database/src/fields/json.ts

@@ -2,18 +2,37 @@ import Field from './field';
 
 export default class JSONField extends Field {
   toDB(value: unknown) {
+    if (value == null) {
+      return null;
+    }
+
+    if (typeof value === 'object') {
       return JSON.stringify(value);
     }
 
+    return value;
+  }
+
   fromDB(value: unknown) {
     try {
       if (typeof value === 'string') {
-        return JSON.parse(value);
+        const parsedValue = JSON.parse(value);
+
+        /**
+         * On Strapi 5 until 5.0.0-rc.6, the values were accidentally stringified twice when saved,
+         * so in those cases we need to parse them twice to retrieve the actual value.
+         */
+        if (typeof parsedValue === 'string') {
+          return JSON.parse(parsedValue);
+        }
+
+        return parsedValue;
       }
     } catch (error) {
       // Just return the value if it's not a valid JSON string
       return value;
     }
+
     return value;
   }
 }