Question: Why AbstractClass._forDB stringify JSON and Array.

Hello, I try to use jugglingdb and can't understand for what function "AbstractClass._forDB" converts object and array to string. This limits search by criterias. We have to use regular expressions or exists another way. Thank for help.

```
AbstractClass._forDB = function (data) {
var res = {};
Object.keys(data).forEach(function (propName) {
var typeName = this.whatTypeName(propName);
if (!typeName && !data[propName] instanceof Array) {
return;
}
if (typeName === 'JSON' || data[propName] instanceof Array) {
res[propName] = JSON.stringify(data[propName]);
} else {
res[propName] = data[propName];
}
}.bind(this));
return res;
};
```

Look at the AbstractClass._forDB function in the codebase, likely in a file like lib/abstract_class.js. Understand how JSON and Array data is handled for different database adapters (redis, mongodb, mysql, etc.). Check if there are existing tests for this function or related search functionality. Determine if the stringification is necessary for all adapters or if it can be conditional.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.