I have this structure:
//////Entity to be filtered
public class StockItem{
#Index
private Ref<StockItemTypeEntity> stockItemType;
} `enter code here`
and
//////Ref
public class StockItemTypeEntity{
#Index
private Ref<StockItemProductTypeEntity> productType;
}
I want to filter StockItem like this:
stockItemQuery = stockItemQuery.filter("stockItemType.productType", fitlerWrapper.getProductType());
But this isn't working. How do I filter using nested Refs?
This is a join, which is not supported by the underlying datastore. That is to say, if you want to perform a join you have to do it yourself.
Depending on the shape of your data and what you are trying to do, one common solution is to denormalize the index data into the parent entity (index a 'productType' field in the StockItem). It does require keeping the data in sync.
Related
I have recently started to use Spring Data MongoDB and I wonder if there is any way to avoid writing entities' attributes explicitly as they are stored in the database. For example, given the following class representing a MongoDB collection:
public class Employee {
#Id
public String id;
private double salary;
...
}
If I want to make a query using MongoTemplate like:
public List findEmployeeBySalaryRange(double salary) {
Query query = new Query();
query.addCriteria(Criteria.where("salary").lt(salary));
...
}
I would like to avoid writing "salary", since that will make the code harder to maintain in the future in case the field name changes. I am thinking of something like getting the field name from the class attribute, but I am not quite sure how. Is there a way to do it? I have looked into the documentation but did not find anything related unless I missed it.
Thanks in advance.
You may create a Utility Class to store all database field names, use #Field annotation on field with constant from that class and use that constant in query to avoid error prone hardcoded Strings.
In Employee Model
#Field(DbFields.SALARY)
private double salary;
In Query,
query.addCriteria(Criteria.where(DbFields.SALARY).lt(salary));
In DbFields Utility class
public static final String SALARY = "salary";
I have a Course entity that contains the following field
#Index
private #Load
Ref<Student> student;
The student entity then has the field
#Index
private String matric;
I want to load all the Course entities sorted using the students matric number.
I have tried using the "." operator to get the sub field like this
ofy().load().type(Course.class).filter("course", course).order("student.matric").list();
but this return no result.
Is it possible to do this? how?
I don't think that is possible with objectify. I would let Course implement Comparable:
#Entity
public class Course implements Comparable<Course> {
.
.
.
#Override
public int compareTo(Course otherCourse) {
return this.getStudent().getMatric().compareTo(otherCourse.getStudent().getMatric());
}
}
Remove the "order" part of the Objectify load and use Collections.sort() instead:
List<Course> courses = ofy().load().type(Course.class).filter("course", course).list();
Collections.sort(courses);
There are no joins in the datastore. If you want to query your Courses by Student properties, you probably will need to denormalize the data into the Course and index it. This means changing the Student data will also require changing Courses.
As an aside: This data model is weird. Are you sure what you're calling Course isn't really an Enrollment?
I am beginning to use Dapper and love it so far. However as i venture further into complexity, i have ran into a big issue with it. The fact that you can pass an entire custom object as a parameter is great. However, when i add another custom object a a property, it no longer works as it tries to map the object as a SQL parameter. Is there any way to have it ignore custom objects that are properties of the main object being passed thru? Example below
public class CarMaker
{
public string Name { get; set; }
public Car Mycar { get; set; }
}
propery Name maps fine but property MyCar fails because it is a custom object. I will have to restructure my entire project if Dapper can't handle this which...well blows haha
Dapper extensions has a way to create custom maps, which allows you to ignore properties:
public class MyModelMapper : ClassMapper<MyModel>
{
public MyModelMapper()
{
//use a custom schema
Schema("not_dbo_schema");
//have a custom primary key
Map(x => x.ThePrimaryKey).Key(KeyType.Assigned);
//Use a different name property from database column
Map(x=> x.Foo).Column("Bar");
//Ignore this property entirely
Map(x=> x.SecretDataMan).Ignore();
//optional, map all other columns
AutoMap();
}
}
Here is a link
There is a much simpler solution to this problem.
If the property MyCar is not in the database, and it is probably not, then simple remove the {get;set;} and the "property" becomes a field and is automatically ignored by DapperExtensions. If you are actually storing this information in a database and it is a multi-valued property that is not serialized into a JSON or similar format, I think you are probably asking for complexity that you don't want. There is no sql equivalent of the object "Car", and the properties in your model must map to something that sql recognizes.
UPDATE:
If "Car" is part of a table in your database, then you can read it into the CarMaker object using Dapper's QueryMultiple.
I use it in this fashion:
dynamic reader = dbConnection.QueryMultiple("Request_s", param: new { id = id }, commandType: CommandType.StoredProcedure);
if (reader != null)
{
result = reader.Read<Models.Request>()[0] as Models.Request;
result.reviews = reader.Read<Models.Review>() as IEnumerable<Models.Review>;
}
The Request Class has a field as such:
public IEnumerable<Models.Review> reviews;
The stored procedure looks like this:
ALTER PROCEDURE [dbo].[Request_s]
(
#id int = null
)
AS
BEGIN
SELECT *
FROM [biospecimen].requests as bn
where bn.id=coalesce(#id, bn.id)
order by bn.id desc;
if #id is not null
begin
SELECT
*
FROM [biospecimen].reviews as bn
where bn.request_id = #id;
end
END
In the first read, Dapper ignores the field reviews, and in the second read, Dapper loads the information into the field. If a null set is returned, Dapper will load the field with a null set just like it will load the parent class with null contents.
The second select statement then reads the collection needed to complete the object, and Dapper stores the output as shown.
I have been implementing this in my Repository classes in situations where a target parent class has several child classes that are being displayed at the same time.
This prevents multiple trips to the database.
You can also use this approach when the target class is a child class and you need information about the parent class it is related to.
I am using Objectify to manage GAE Datastore for my GWT app. The problem is that I am not using queries properly and I get UmbrellaExceptions as per below:
Caused by: java.lang.RuntimeException: Server Error: java.lang.String cannot be cast to java.lang.Number
at com.google.web.bindery.requestfactory.shared.Receiver.onFailure(Receiver.java:44)
Say that I have a class Box with a unique field String id. I want to get the Box object whose id == "cHVQP6zZiUjM"
This is how I do it now:
public Box getBox(String boxId)
{
Objectify ofy = ObjectifyService.begin();
Query<Box> q=ofy.query(Box.class).filter("id",boxId);
Box targetBox = q.get();
return targetBox;
}
#Entity
public class Box extends DatastoreObject{
private String id;
private String title;
}
I tried doing this with ofy.load() but that method is not defined in my class Objectify (I don't know why).
Your key is encoded. Try using:
Box targetBox = ofy.get(Box.class, KeyFactory.stringToKey(boxId));
To decode your key.
The short answer: You are missing the #Id annotation in your entity.
The long answer: Id fields are special in the datastore. The id is not a real property, but rather a part of the Key that identifies the entity. You can't really filter on id fields, but you can filter on a special field called __key__. Objectify is somewhat clever about letting you filter by the id field and converting this to a __key__ filter under the covers, but it can't do it if you don't annotate the entity properly!
Actually I'm a little confused because Objectify shouldn't let you register the entity without an #Id field.
By the way, there are two sections of the documentation: Objectify4 (release coming soon) and Objectify3. Since you're using Ofy3, there is no load() method.
Another thing: Get-by-key operations are strongly preferred to queries when the operations are equivalent (as they are in your example).
This is my first question on any of these websites so pardon my unprofessionalism.
I use playframework with SIENA module (with GAE) and I came accross the following problem:
Given 3 entities:
public class Meeting extends Model{
#Id
public Long id;
public String place;
#Owned
Many<MeetingUser> users;
.
.
.
}
public class User extends Model{
#Id
public Long id;
public String firstName;
public String lastName;
#Owned
Many<MeetingUser> meetings;
.
.
.
}
public class MeetingUser extends Model{
#Id
public Long id;
public Meeting meeting;
public User user;
.
.
.
public User getUser(){
return Model.all(User.class).filter("id", user).get();
}
public Meeting getMeeting(){
return Model.all(Meeting.class).filter("id", meeting).get();
}
}
For instance I am listing a meeting and all their users:
public static void meetingInfo(Long meetingId){
Meeting meeting = Models.all(Meeting.class).filter("id",meetingId);
List<MeetingUser> meetingusers = meeting.asList();
List<User> users = new ArrayList<User>();
for(MeetingUser mu: meetingusers){
users.add(mu.getUser());
}
render(users);
}
This is done(is there any better way here?) however when it comes to filtering (especially dynamic filtering for many many fields) I can not use the Query's filter method on the MeetingUser as I need to filter on a MeetingUser's field's field (firstName). The same problem arise for ordering. I need the solution for both problems.
I hope my problem is clear and I appreciate any kind of help here.
Remember that you are in GAE which is a NoSQL DB.
So you can't do Join request as in RDBMS.
Yet, this is not really the pb you have so this was just to be sure you are aware of it ;)
So if you want to find the person having given firstname in a given meeting, can you try the following:
List<MeetingUser> meetingusers = meeting.users.asQuery().filter("firstname", "XXX");
(you can also order)
Nevertheless, knowing that you can't join, remember that you can't write a query searching for a meeting in which there are users whose firstname is XXX as it would require some joins and it doesn't exist in GAE. In this case, you need to change your model following NoSQL philosophy but this is another subject
regards
Let's try to give a way to do what you want...
Your relation is a Many-to-Many which is always the worst case :)
You want to filter Meeting by User's firstname.
It requires a join request which is not possible in GAE. In this case, you must change your model by denormalizing it (sometimes use redundancy also) and manage the join by yourself. Actually, you must do the job of the RDBMS by yourself. It seems overkill but in fact, it's quite easy. The only drawback is that you must perform several requests to the DB. NoSQL means No Schema (& No Join) so there are a few drawbacks but it allows to scale and to manage huge data load... it depends on your needs :)
The choice you did to create the MeetingUser which is a "joined" table and a kind of denormalization is good in GAE because it allows to manage the join yourself.
Solution:
// fetch users by firstname
List<User> users = users.all().filter("firstName", "John").fetch();
// fetch meetingusers associated to these users (verify the "IN" operator works because I didn't use that for a long time and don't remember if it works with this syntax)
List<MeetingUser> meetingusers = MeetingUser.all().filter("user IN", users);
// now you must fetch the whole meeting because in MeetingUser, only the Meeting ID is stored (other fields are Null or O)
List<Meeting> meetings = new ArrayList<Meeting>()
for(MeetingUsers mu:meetingusers) {
meetings.add(meetingusers.meeting);
}
// use the batch feature to fetch all objects
Meeting.batch(Meeting.class).get(meetings);
// you have your meetings
Hope this helps!