I'm struggling with the include function in RavenDB. In my model I have a blog post that holds a list of comments. The comment class that's used in this list holds a reference to a user.
public class BlogPost
{
public string Id { get; set; }
public List<Comment> Comments { get; set; }
public BlogPost()
{
Comments = new List<Comment>();
}
}
public class Comment
{
public string Id { get; set; }
public string Text { get; set; }
public string UserId { get; set; }
}
What I want to do is to get the blogpost and get a list of comments with the details of the user that wrote the comment to display in the UI, without querying the server for every single user (N+1).
I would be happy with some pointers on how to solve this. Thanks!
You can do that using something like:
session.Include<BlogPost>(b=>b.Comments.Select(x=>x.UserId)).Load(1);
I think this page would answer your question.
You can load multiple documents at once:
var blogSpots = session.Include<BlogPost>(x => x.Comments.Select(x=>x.UserId))
.Load("blogspot/1234", "blogspot/4321");
foreach (var blogSpot in blogSpots)
{
foreach (var userId in blogSpot)
// this will not require querying the server!!!
var cust = session.Load<User>(userId);
}
Related
I'm working with two different aggregate roots: Post and Question. Both of them have a Category.
So far I have implemented it as a shared entity (which I'm not sure if is a correct design in DDD).
public class Post
{
public Guid Id { get; private set; }
public Category Category { get; private set; }
public string Title { get; private set; }
public string Body { get; private set; }
}
public class Question
{
public Guid Id { get; private set; }
public Category Category { get; private set; }
public string Title { get; private set; }
public string Body { get; private set; }
}
public class Category
{
public int Id { get; private set; }
public string Name { get; private set; }
public string Key { get; private set; }
}
Note: I'm aware I'm falling into primitive obsession anti-pattern, and I have plans on refactor the primitives into ValueObjects.
After read this post DDD: Share entity with multiple aggregate roots I'm thinking that maybe I should convert the Category in a ValueObject (with multiple fields).
In theory Category could be an Entity with its own lifecycle, but reality is that I don't really add/remove/update categories.
Is it possible to use a shared Entity on DDD? Or I better rather use a ValueObject?
Lets deal with one aggregate first: Post
Now to answer your question:
Is it possible to use a shared Entity on DDD? Or I better rather use a ValueObject?
It depends on what you will do with Category.
Scenario 1:
You have a feature(or page) in your application to show all posts of a category. I would go with the following design:
public class Category
{
public int Id { get; set; }
//this is my in-memory database. Use repository and service to adjust yours
public static List<Post> Posts;
public Category()
{
Posts = new List<Post>();
}
public void AddPost(Guid id, string title, string body)
{
var post = new Post(id, title, body, this.Id);
//saving the post into in-memory. Perhaps you can check some business logic inside Post entity
Posts.Add(post);
}
// You can retrieve all posts of a single category
public IEnumerable<Post> GetAllPosts()
{
return Posts.Where(x => x.CategoryId == this.Id);
}
}
public class Post
{
public Guid Id { get; private set; }
public string Title { get; private set; }
public string Body { get; private set; }
public int CategoryId { get; private set; }
public Post(Guid id)
{
Id = id;
}
public Post(Guid id, string title, string body, int categoryId)
{
//I prefer to pass guid into domain from external services.
//Using this way, your service will have the id to return to upper layers.
//Alternatively you can create new guid here on your own
Id = id;
Title = title;
Body = body;
CategoryId = categoryId;
}
// you can retrieve a post detail
public Post GetPost()
{
return Category.Posts.FirstOrDefault(x => x.Id == this.Id);
}
}
I can see only one aggregate root in this scenario: Category.
Scenario 2:
You have posts page, from there users can view detail post. Additionally, every post has a category which will be shown somewhere on that detailed page. You can have following simple design:
public class Post
{
public Guid Id { get; private set; }
public string Title { get; private set; }
public string Body { get; private set; }
public string CatKey { get; private set; }
public Post(Guid id)
{
Id = id;
}
public Post(Guid id, string title, string body, string catKey)
{
//I prefer to pass guid into domain from external services.
//Using this way, your service will have the id to return to upper layers.
//Alternatively you can create new guid here on your own
Id = id;
Title = title;
Body = body;
//I don't even bother with category id. This is a simple value object, you can store all of your categories
//into a hashtable of key-value
CatKey = catKey;
}
// you can retrieve a post detail
public Post GetPost()
{
//get your post detail from repo
}
}
Hope you can make your decision now.
The main question of Entity vs ValueObject is would two instances of the Category with the same values need to be tracked differently? The classic example is a dollar bill - in most instances, the serial number (ID) doesn't matter, and one dollar is the same as another (ValueObject). If your domain is collecting rare bills, though, that would change.
I'd suspect not in your case, since it appears Category is really just comprised of the name and key. If the Category of a Post changes, do you need to track what the Category previous was?
Let's say we have a document like this
public class Event
{
public string Id { get; set; }
public EntityDescriptor Venue { get; set; }
// Other properties omitted for simplicity
}
public class EntityDescriptor
{
public string Id { get; set; }
public string Name { get; set; }
}
And an index like this
public class Events : AbstractIndexCreationTask<Event>
{
public Events()
{
Map = items => from e in items
select new
{
Venue_Id = e.Venue.Id,
Venue_Name = e.Venue.Name
};
}
}
When trying to sort on Event.Venue.Id
session.Query<Event, Events>().Take(10).OrderBy(e => e.Venue.Id).ToArray();
the sent request is
/indexes/Events?&pageSize=10&sort=__document_id&SortHint-__document_id=String
Is this by design or a bug?
PS: OrderBy(e => e.Venue.Name) works as expected (sort=Venue_Name).
It's not a bug. __document_id is the special known field containing the ID of the document. It's there regardless of whether you have an .Id property.
edit
I misread your question. This indeed appears to be a bug. I recommend you send a simple repro case to the Raven forum and let them know which RavenDB version you're using.
Example: Let’s assume the following collections. ThrashMetalDocumentsCollection and SpeedMetalDocumentsCollection, both collections having the same HeavyMetalRecordDocument structure as shown below. How do I query and return ALL of the records in both collections and sort them by releaseDate (oldest first) and rating (high to low)? Thanks! \m/ \m/
static async Task getAllRecords()
{
var builder = Builders<HeavyMetalRecordDocument>.Filter;
//var filter;
using (var cursor = await ThrashMetalDocumentsCollection.Find()
.Sort(Builders<HeavyMetalRecordDocument>.Sort.Ascending(x => x.rating))
.ToCursorAsync())
{
while (await cursor.MoveNextAsync())
{
foreach (var doc in cursor.Current)
{
//Do Something…
}
}
}
}
public class HeavyMetalRecordDocument
{
public ObjectId Id { get; set; }
public String artist { get; set; }
public String title { get; set; }
public DateTime releaseDate { get; set; }
public int rating { get; set; } // 1-10
}
MongoDB is not a relational database, and as such, it cannot perform joins (which is what you are trying to accomplish). You probably want to think more about the structure of your database. Without knowing any more about what you are trying to do, I would suggest putting all types of albums into a single collection - putting in an additional field indicating the genre of the album.
The only examples I can find addressing this sort of scenario are pretty old, and I'm wondering what the best way is to do this with the latest version of ORMLite...
Say I have two tables (simplified):
public class Patient
{
[Alias("PatientId")]
[Autoincrement]
public int Id { get; set; }
public string Name { get; set; }
}
public class Insurance
{
[Alias("InsuranceId")]
[Autoincrement]
public int Id { get; set; }
[ForeignKey(typeof("Patient"))]
public int PatientId { get; set; }
public string Policy { get; set; }
public string Level { get; set; }
}
Patients can have multiple Insurance policies at different "levels" (primary, secondary, etc). I understand the concept of blobbing the insurance information as a Dictionary type object and adding it directly to the [Patient] POCO like this:
public class Patient
{
public Patient() {
this.Insurances = new Dictionary<string, Insurance>(); // "string" would be the Level, could be set as an Enum...
}
[Alias("PatientId")]
[Autoincrement]
public int Id { get; set; }
public string Name { get; set; }
public Dictionary<string, Insurance> Insurances { get; set; }
}
public class Insurance
{
public string Policy { get; set; }
}
...but I need the insurance information to exist in the database as a separate table for use in reporting later.
I know I can join those tables in ORMLite, or create a joined View/Stored Proc in SQL to return the data, but it will obviously return multiple rows for the same Patient.
SELECT Pat.Name, Ins.Policy, Ins.Level
FROM Patient AS Pat JOIN
Insurance AS Ins ON Pat.PatientId = Ins.PatientId
(Result)
"Johnny","ABC123","Primary"
"Johnny","987CBA","Secondary"
How can I map that into a single JSON response object?
I'd like to be able to map a GET request to "/patients/1234" to return a JSON object like:
[{
"PatientId":"1234",
"Name":"Johnny",
"Insurances":[
{"Policy":"ABC123","Level":"Primary"},
{"Policy":"987CBA","Level":"Secondary"}
]
}]
I don't have a lot of hope in this being do-able in a single query. Can it be done in two (one on the Patient table, and a second on the Insurance table)? How would the results of each query be added to the same response object in this nested fashion?
Thanks a ton for any help on this!
Update - 4/29/14
Here's where I'm at...In the "Patient" POCO, I have added the following:
public class Patient
{
[Alias("PatientId")]
[Autoincrement]
public int Id { get; set; }
public string Name { get; set; }
[Ignore]
public List<Insurance> Insurances { get; set; } // ADDED
}
Then, when I want to return a patient with multiple Insurances, I do two queries:
var patientResult = dbConn.Select<Patient>("PatientId = " + request.PatientId);
List<Insurance> insurances = new List<Insurance>();
var insuranceResults = dbConn.Select<Insurance>("PatientId = " + patientResult[0].PatientId);
foreach (patientInsurance pi in insuranceResults)
{
insurances.Add(pi);
}
patientResult[0].Insurances = insurances;
patientResult[0].Message = "Success";
return patientResult;
This works! I get nice JSON with nested items for Insurances while maintaining separate related tables in the db.
What I don't like is that this object cannot be passed back and forth to the database. That is, I can't use the same nested object to automatically insert/update both the Patient and InsurancePolicy tables at the same time. If I remove the "[Ignore]" decorator, I get a field in the Patient table called "Insurances" of type varchar(max). No good, right?
I guess I'm going to need to write some additional code for my PUT/POST methods to extract the "Insurances" node from the JSON, iterate over it, and use each Insurance object to update the database? I'm just hoping I'm not re-inventing the wheel here or doing a ton more work than is necessary.
Comments would still be appreciated! Is Mythz on? :-) Thanks...
An alternate more succinct example:
public void Put(CreatePatient request)
{
var patient = new Patient
{
Name = request.Name,
Insurances = request.Insurances.Map(x =>
new Insurance { Policy = i.Policy, Level = i.Level })
};
db.Save<Patient>(patient, references:true);
}
References are here to save the day!
public class Patient
{
[Alias("PatientId")]
[Autoincrement]
public int Id { get; set; }
public string Name { get; set; }
[Reference]
public List<Insurance> Insurances { get; set; }
}
public class Insurance
{
[Alias("InsuranceId")]
[Autoincrement]
public int Id { get; set; }
[ForeignKey(typeof("Patient"))]
public int PatientId { get; set; }
public string Policy { get; set; }
public string Level { get; set; }
}
I can then take a JSON request with a nested "Insurance" array like this:
{
"Name":"Johnny",
"Insurances":[
{"Policy":"ABC123","Level":"Primary"},
{"Policy":"987CBA","Level":"Secondary"}
]
}
...to create a new record and save it like this:
public bool Put(CreatePatient request)
{
List<Insurance> insurances = new List<Insurance>();
foreach (Insurance i in request.Insurances)
{
insurances.Add(new Insurance
{
Policy = i.Policy,
Level = i.Level
});
}
var patient = new Patient
{
Name = request.Name,
Insurances = insurances
};
db.Save<Patient>(patient, references:true);
return true;
}
Bingo! I get the new Patient record, plus 2 new records in the Insurance table with correct foreign key references back to the PatientId that was just created. This is amazing!
First you should define a foreign collection in Patient class. (with get and set methods)
#ForeignCollectionField
private Collection<Insurance> insurances;
When you query for a patient, you can get its insurances by calling getInsurances method.
To convert all into a single json object with arrays inside you can use a json processor. I use Jackson (https://github.com/FasterXML/jackson) and it works very well. Below will give you json object as a string.
new ObjectMapper().writeValueAsString(patientObject);
To correctly map foreign fields you should define jackson references. In your patient class add a managed reference.
#ForeignCollectionField
#JsonManagedReference("InsurancePatient")
private Collection<Insurance> insurances;
In your insurance class add a back reference.
#JsonBackReference("InsurancePatient")
private Patient patient;
Update:
You can use Jackson to generate objects from json string then iterate and update/create database rows.
objectMapper.readValue(jsonString, Patient.class);
public class PersonBrief
{
public int Id { get; set; }
public string Picture { get; set; }
public PersonBrief(Person person)
{
Id = person.Id;
Picture = person.Picture;
}
}
public class Person : PersonBrief
{
public string FullName { get; set; }
}
var results = session.Query<Person>()
.Select(x => new PersonBrief(x))
.ToList();
Assert.IsNull(results[0] as Person); // Fails
Is this a bug? If not, what would be the correct way to select only the fields i'm interested in?
It would work if you move the .ToList before the .Select, but that would be doing the work on the client.
If you want to do it on the server, you need to use As in your query, and you need a static index that does a TransformResults. See these docs.