I am curious about what methods do you use for complex searching with NHibernate ?
I am using Ayende's
What is yours ?
Thanks for your advices and answers.
If we have a complex dynamic search, we will usually construct a SearchParameter object and then pass that into a method that will build our criteria for us.
For example, if we were searching for a person we might have a search object that looks like this:
public class PersonSearchParameters
{
public string FirstName {get; set;}
public string LastName {get; set;}
public ICriteria GetSearchCriteria()
{
DetachedCriteria query = DetachedCriteria.For(typeof (Person));
//Add query parameters
Return query;
}
}
Then for each type of search, we'll be able to create the single criteria from the class, or we could have multple search parameter classes and chain them together
We use HQL, but we're still trying to wrap our heads around the Criteria API for complex queries. We have to manage a lot of duplication when using HQL.
I use pretty much Ayende's too jsut a bit more complex, what do you want to do that you cant do with that?
Basically what we added is that we have an interface where we define all the fields where we want to search and we call this when we are about to make the search which means that we can easily change what we are searching for.
Also we are using Active Record in the project ( on top of Hibernate) and tis pretty cool, loads of tasks gets simplified , thou the lack of docs does hurt sometimes
Cheer
Related
I have a project using NH 3.1 and have been using the QueryOver syntax for everything thus far.
One aspect of this project lives in a organization-wide database that I have read-only access to and is using a completely differently DBMS (Oracle vs MSSQL). So I store references from my objects (Foos) to their objects (Bars) using a standard many-to-many table
FooBars
FooID int not null PK
BarID int not null PK
And my domain object, instead of having a Iset<Bar> instead has an ISet<int> BarIDs which is manually mapped to the FooBars table. This prevents NH from trying to do the impossible and join all the way over to the Bars table (I can use a BarRepository.Get() to retrieve the details of the Bars later, if I need them, and in this case, I wouldn't, because I just need the IDs to filter the list of objects returned).
Given IList<int> SelectedBars how can I write a QueryOver<Foo> where BarIDs contains any element in SelectedBars?
SQL something like
...FROM foos INNER JOIN foobars on foo.fooID = foobars.fooID WHERE barID IN ( ... )
It is not possible with QueryOver. Two years ago, I had a similar question about filtering value collections. (Note: QueryOver is based on Criteria API).
I'm not 100% sure, but it probably works with HQL. It is much more powerful.
You may include an SQL statement into the QueryOver criteria.
I don't really understand why you don't map it as a list of entities. There is lazy loading to avoid unnecessary loading - although there are some trade offs sometimes. You can access the ID of NH proxies without hitting the database. Mapping ids makes usually life much harder.
Try:
session.QueryOver<Foo>()
.JoinQueryOver(x => x.FooBars)
.WhereRestrictionOn(x => x.BarId).IsIn( ... )
So 3 years later, I'm back to report how I did solve this.
public class Foo :Entity {
public virtual ISet<FooBar> BarIDs { get; protected internal set; }
} ...
public class FooBar :Entity {
protected internal FooBar() { }
protected internal FooBar(Foo f, int BarID) { ... }
public virtual Foo Foo { get; protected internal set; }
public virtual int BarID { get; protected internal set; }
}
This is basically what Stefan suggested, and what's hinted at in the related post. You just have to eat the overhead of writing an extra entity and referencing it. Remember that I'm storing BarIDs instead of full Bar objects, because I'm dealing with a hard boundary between two databases: the Bars are stored in an entirely different database on a different platform than the Foos. Otherwise of course, you're far better off just telling Foo that is has an ISet<Bar>.
Finding Foos by SelectedBarIDs is then easy, much like Thilak suggested:
session.QueryOver<Foo>().JoinQueryOver<FooBar>(f => f.BarIDs).
WhereRestrictionOn(b => b.BarID).IsIn(...)...
It's an interesting problem, working across the database boundary like this. I can't say I like having to do it, but if someone else is going to take the time to maintain a list of Bars and make it available for my use, it would be a giant waste of resources for me to do the same. So a small inefficiency in having the wrapper class is a very easy cost to justify.
Using NHibernate, I need to be able to configure my application to sort a specific collection of entities exactly as needed.
The configurable sort:
can involve multiple properties
can specify the sorted properties in any order
can specify asc/desc on the sorted properties
can sort by custom properties (i.e. there is no corresponding SQL/C# property - it is calculated)
This functionality is inherited from an existing app where parts of the SQL are specified by an administrator and the SQL statement is built/executed dynamically.
Every time I try thinking through a solution I start getting in muddy waters with all kinds of alarms going off in my head regarding maintainability, performance, scalability, security, etc..
For example, I figure the admin can specify a comma delimited string like so:
"Date asc, FirstName asc, LastName desc"
I can split the string and go through a loop matching the property/sort pairings in a case statement and calling .AddOrder(Order.Asc("FirstName")) as necessary. But then, how do I handle custom properties? I could allow the user to specify SQL for calculating custom properties and then allow the user to sort on those like they would FirstName, but I'm seemingly back at dirty/kludge again.
Is there a clean/appropriate way to handle this requirement?
After much thought and a stroke of luck, I may have a solution.
public class CustomOrder : Order
{
private string customOrderSql;
public CustomOrder(string customOrderSql) : base("", true)
{
this.customOrderSql = customOrderSql;
}
public override NHibernate.SqlCommand.SqlString ToSqlString(
ICriteria criteria, ICriteriaQuery criteriaQuery)
{
return new NHibernate.SqlCommand.SqlString(this.customOrderSql);
}
}
I can pass a custom sort string to my repository where I add my CustomOrder as follows:
.AddOrder(new CustomOrder(customSort))
I still can't sort by custom properties but maybe I can get away with applying case statements in the order by clause. I'm still open for better suggestions if they exist.
This is a follow on question to My earlier question on lazy loading properties. Since the application is an enhancement to a production application in a fairly major enterprise, and it currently running using NHib 1.2, upgrading to version 3 is not going to happen, so the suggested answer of using Lazy Properties in 3.0 won't work for me.
To summarize the problem, I have simple database with 2 tables. One has about a dozen simple fields, plus a one to many relation to the second table as a child table. Two of the fields are very large blobs (several megabytes each), and I want to, effectively, lazy load them. This table has about 10 records, and they populate a grid at start up, but access to the large blobs are only needed for whatever row is selected.
The object structure looks something like this:
[Serializable]
[Class(Schema = "dbo", Lazy = false)]
public class DataObject
{
[Id(-2, Name = "Identity", Column="Id")]
[Generator(-1, Class="native")]
public virtual long Identity { get; set;}
[Property]
public string FieldA { get; set;}
[Property]
public byte[] LongBlob {get; set;}
[Property]
public string VeryLongString { get; set;}
[Bag(-2, Cascade=CascadeStyle.All, Lazy= false, Inverse=true)]
[Key(-1, Column="ParentId")]
[OneToMany(0, ClassType=typeof(DataObjectChild))]
public IList<DataObjectChild> ChildObjects { get; set;}
}
Currently, the table is accessed with a simple query:
objectList = (List<DataObject>) Session.CreateQuery("from DataObject").List<DataObject>();
And that takes care of everything, including loading the child objects.
What I would like is a query to do exactly the same thing, except select a list of the properties of the DataObject that includes everything EXCEPT the two blobs. Then I can add custom property Getters that will go out and load those properties when they are accessed.
So far, I have not been successful at doing that.
Things I have tried:
a) constructing an HQL query using a SELECT list.
It looks something like this:
objectList = (List<DataObject>) Session.CreateQuery(
"SELECT new DataObject " +
"(obj.Identity, obj.FieldA) " +
"from DataObject as obj")
That works, though I have to add a constructor to the DataObject that will construct it from fields I select, which is rather cumbersome. But then it doesn't load and expand the list of child objects, and I can't figure out how to do that easily (and don't really want to - I want to tell NHib to do it.)
b) removing the [Property] attribute from the two fields in the object definition. That keeps the NHibernate.Mapping.Attributes from mapping those fields, so they don't get included in the query, but then I have no way to access them from NHib at all, including writing them out when I go to save a new or modified DataObject.
I'm thinking there has to be an easier way. Can somebody point me in the right direction?
Thanks
I think you're on the right path. However, you're going to have to do more manual work since you're using a very old version of NHibernate. I would fetch projections of your entities that contain only the columns you want to eagerly load. Then when the UI requests the large blob objects, you're going to have to write another query to get them and supply them to the UI.
Another option would be to have a second class (e.g. SmallDataObject) with the same mapping (but without the blobs) and use that for the list. When editing a list item you would load the class with the blobs using the id of the selected list item.
In any case, modifying the mapping after the creation of the SessionFactory is not possible, so you cannot get rid of the mapped properties on demand.
I am trying to map a domain model in NHibernate. The domain model is implemented with what I think is DDD style. The mapping works mostly but then when I try to use a collection filter on an a collection I get an exception which says: The collection was unreferenced.
I know the problem comes from how I've implemented the collection. My question: Is it possible to use collection filters in nHibernate on collections implemented this way or should I just forget it, i.e. nHibernate cannot work with this.
The code is as follows:
Person
{
IList<Address> _addresses = new List<Address>();
public string FirstName {get; set;}
...
public void addAddress(Address address)
{
// ... do some checks or validation
_addresses.Add(address);
}
public void removeAddress(Address address) {...}
public ReadOnlyCollection<Address> Addresses
{
get { return new ReadOnlyCollection<Address>(_addresses); }
}
}
The main issue is that I don't want to expose the internal addresses collection publicly.
Every other thing works, I use the field.camelcase-underscore access so nHibernate interacts directly with the field. I've been working through the Hibernate in Action book, an now I'm in chapter 7 where it deals with collection filters.
Is there any way around this. I've got it to work by exposing the internal collection like this:
public ReadOnlyCollection<Address> Addresses
{
get { return _addresses; }
}
but I really dont want to do this.
Help would really be appreciated.
Jide
If I recall correctly - NHibernate filter works as additional clause in sql queries to reduce returned rows from db.
My question to You is - why do You need that?
I mean - how much addresses one person might have? 1? 5? 10?
About collection isolation...
I myself just accept it as a sacrifice for NHibernate (just like argument-less ctor's and "virtual`ity") and use exposed IList everywhere (with private setters) just to reduce technical complexity. Their contents surely can be modified from outside, but I just don't do that.
It's more important to keep code easily understandable than making it super safe. Safety will follow.
What is the recommended way to return ad hoc (custom case by case) data from repository which don't fit any model entities or which extend some?
The 101 example would be the ubiquitous hello word application: a blog system. Suppose you want to load a list of posts where post entry has some additional information which does not exists in the Post entity. Let’s say it is the number of comments and the date and time of the last comment. This would be highly trivial if one was using the plain old SQL and reading data directly from the database. How am I supposed to do it optimally using the repository pattern if I cannot afford loading the entire collections of Comments for each Post, and I want to do it in one database hit? Is there any commonly used pattern for this situation? Now imagine that you have moderately complex web application where each page needs a slightly different custom data, and loading full hierarchies is not possible (performance, memory requirements etc).
Some random ideas:
Add a list of properties to each model which could be populated by the custom data.
Subclass model entities case by case, and create custom readers for each subclass.
Use LINQ, compose ad hoc queries and read anonymous classes.
Note: I’ve asked a similar question recently, but it seemed to be too general and did not attract much attention.
Example:
Based on suggestions in answers below, I am adding a more concrete example. Here is the situation I was trying to describe:
IEnumarable<Post> posts = repository.GetPostsByPage(1);
foreach (Post post in posts)
{
// snip: push post title, content, etc. to view
// determine the post count and latest comment date
int commentCount = post.Comments.Count();
DateTime newestCommentDate = post.Comments.Max(c => c.Date);
// snip: push the count and date to view
}
If I don’t do anything extra and use an off the shelf ORM, this will result to n+1 queries or possibly one query loading all posts and comments. But optimally, I would like to be able to just execute one SQL which would return one row for each post including the post title, body etc. and the comment count and most recent comment date in the same. This is trivial in SQL. The problem is that my repository won’t be able to read and fit this type of data into the model. Where do the max dates and the counts go?
I’m not asking how to do that. You can always do it somehow: add extra methods to the repository, add new classes, special entities, use LINQ etc., but I guess my question is the following. How come the repository pattern and the proper model driven development are so widely accepted, but yet they don’t seem to address this seemingly very common and basic case.
There's a lot to this question. Are you needing this specific data for a reporting procedure? If so, then the proper solution is to have separate data access for reporting purposes. Flattened databases, views, ect.
Or is it an ad-hoc query need? If so, Ayende has a post on this very problem. http://ayende.com/Blog/archive/2006/12/07/ComplexSearchingQueryingWithNHibernate.aspx
He utilizes a "Finder" object. He's using NHibernate, so essentially what he's doing is creating a detached query.
I've done something similar in the past by creating a Query object that I can fill prior to handing it to a repository (some DDD purist will argue against it, but I find it elegant and easy to use).
The Query object implements a fluent interface, so I can write this and get the results back:
IQuery query = new PostQuery()
.WithPostId(postId)
.And()
.WithCommentCount()
.And()
.WithCommentsHavingDateLessThan(selectedDate);
Post post = _repository.Find(query);
However, in your specific case I have to wonder at your design. You are saying you can't load the comments with the post. Why? Are you just being overly worrisome about performance? Is this a case of premature optimization? (seems like it to me)
If I had a Post object it would be my aggregate root and it would come with the Comments attached. And then everything you want to do would work in every scenario.
Since we needed to urgently solve the issue I outlined in my original question, we resorted to the following solution. We added a property collection (a dictionary) to each model entity, and if the DAL needs to, it sticks custom data into to. In order to establish some kind of control, the property collection is keyed by instances of a designated class and it supports only simple data types (integers, dates, ...) which is all we need at movement, and mostly likely will ever need. A typical case which this solves is: loading an entity with counts for its subcollections instead of full populated collections. I suspect that this probably does not get any award for a software design, but it was the simplest and the most practical solution for our case.
Can't say I really see what the problem is, just firing in the air here:
Add a specific entity to encapsulate the info yo want
Add a property Comments to the Post. (I don't see why this would require you to fetch all comments - you can just fetch the comments for the particular post you're loading)
Use lazy loading to only fetch the comments when you access the property
I think you would have a greater chance of seeing your question answered if you would make platform, language and O/R mapper specific (seems to be .NET C# or VB, since you mentioned LINQ. LINQ 2 SQL? Entity framework? Something else?)
If you aren't locked into a RDBMs then a Database like CouchDB or Amazons SimpleDB might be something to look at. What you are describing is trivial in a CouchDB View. This probably doesn't really answer you specific question but sometimes it's good to look at radically different options.
For this I generally have a RepositoryStatus and a Status class that acts as my Data Transfer Object (DTO). The Status class is used in my application service layer (for the same reason) from which the RepositoryStatus inherits. Then with this class I can return error messages, response objects, etc. from the Repository layer. This class is generic in that it will accept any object in and cast it out for the receiver.
Here is the Status class:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using RanchBuddy.Core.Domain;
using StructureMap;
namespace RanchBuddy.Core.Services.Impl
{
[Pluggable("Default")]
public class Status : IStatus
{
public Status()
{
_messages = new List<string>();
_violations = new List<RuleViolation>();
}
public enum StatusTypes
{
Success,
Failure
}
private object _object;
public T GetObject<T>()
{
return (T)_object;
}
public void SetObject<T>(T Object)
{
_object = Object;
}
private List<string> _messages;
public void AddMessage(string Message)
{
_messages.Add(Message);
}
public List<string> GetMessages()
{
return _messages;
}
public void AddMessages(List<string> Messages)
{
_messages.AddRange(Messages);
}
private List<RuleViolation> _violations;
public void AddRuleViolation(RuleViolation violation)
{
_violations.Add(violation);
}
public void AddRuleViolations(List<RuleViolation> violations)
{
_violations.AddRange(violations);
}
public List<RuleViolation> GetRuleViolations()
{
return _violations;
}
public StatusTypes StatusType { get; set; }
}
}
And here is the RepositoryStatus:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using RanchBuddy.Core.Services.Impl;
using StructureMap;
namespace RanchBuddy.Core.DataAccess.Impl
{
[Pluggable("DefaultRepositoryStatus")]
public class RepositoryStatus : Status, IRepositoryStatus
{
}
}
As you can see the RepositoryStatus doesn't yet do anything special and just relies on the Status objects utilities. But I wanted to reserve the right to extend at a later date!
I am sure that some of the die-hards out there will state that this should not be used if you are to be a prueist...however I know your pain in that sometimes you need to pass out more than just a returned object!