In NHibernate, Is it possible to do a look up based on an entity passed?
I would like to pass an object from the ui and do a look up based on its values instead of having multiple methods for each possible variation.
For example if I pass a user with the firstname 'John', I'd like to return all users with that firstname.
Any hints much appreciated.
You can use Find by example method in Nhibernate.
Here :
var user=new User();
user.Firstname="John";
var criteria=session.CreateCriteria(typeof(User)).Add(Example.Create(user));
Example is a special kind of expression that builds criterion based on provided entity.
Related
I have a node Country. I know that this node has some properties, but I don't know which. I mean, I know since I've take a look at model. Here is what I've found in documentation:
Country
name: String
iso_2_code: String
iso_3_code: String
region: String
sub.region: String
I know that if I run
MATCH (c:Country)
RETURN c.iso_2_code
I'll get result for one specific property. Is there a query that would as a result return me something like: name, iso_2_code, iso_3_code, region, sub.region?
If I didn't have access to the model how could I list all of the properties that are attached to some node type?
Answering more from a Cypher or openCypher perspective than for a specific implementation. Using the air-routes dataset. There are three things to consider.
Firstly if you know the properties you want, as you mentioned, you can just ask for them explicitly.
MATCH (a:airport {icao:'KDFW'})
RETURN a.city, a.desc
However, if you want all properties, but do not want to list them all, you can just do:
MATCH (a:airport {icao:'KDFW'})
RETURN properties(a)
If you just want the property keys:
MATCH (a:airport {icao:'KDFW'})
RETURN keys(properties(a))
Lastly, if you want the properties plus the label and ID information you can just do:
MATCH (a:airport {icao:'KDFW'})
RETURN a
In my SDN 4 project I have a following Cypher query(a part of query):
(entity)<-[:COMMENTED_ON]-(comg:CommentGroup)
for example I can get id of entity with a following Cypher function id(entity)
How to get entity name or class name ?
Use the labels function
match (entity)<-[:COMMENTED_ON]-(comg:CommentGroup) return id(entity), labels(entity)
For each row returned, you'll get the Neo4j id and array of labels.
Assuming your NodeEntity class labels match at least one of these labels, you can then iterate and load the appropriate class instance yourself.
Generally speaking you shouldn't need to do this however.
If (entity) is polymorphic, SDN/OGM will hydrate the correct objects for you. It pretty much does under the hood what I described above, but it also handles matching on interfaces, subclasses, etc.
I've created an Arraylist for Employee class and initialized values for the data members like Empid,Empname,DOJ,Salary...after initializing I want to sort with respect to any one particular field. Is this possible in collections or in any concept?
Thanks in advance
If you are using c# and Linq you can try with:
var List = TheList.OrderBy(p => p.Empid);
I believe that linq(in c#) has this orderby extension method
List<MyObj> ol = myList.OrderBy(myOb => myOb.AProperty).ToList();
Java:
If you always want to sort on the same field, have your class Employee implement Comparable<Employee>. Than you can use Collections.sort(List)
If you want to sort on different Field, implement different Comparator classes and use Collections.sort(List, Comparator)
... In C#, this is very easily doable via Linq - Also look here for more examples.
Can someone tell me why in NHibernate mapping we can set access="field.camelcase", since we have access="field" and access="property"?
EDIT: my question is "why we can do this", not "what does it mean". I think this can be source of error for developper.
I guess you wonder what use field.camelcase have when we can do the same with just field? That's true, but that would give (NH) properties unintuive names when eg writing queries or reference the property from other mappings.
Let's say you have something you want to map using the field, eg
private string _name;
public string Name { get { return _name; } }
You sure can map the field using "field" but then you would have to write "_name" when eg writing HQL queries.
select a from Foo a where a._name = ...
If you instead using field.camelcase the data, the same query would look like
select a from Foo a where a.Name...
EDIT
I now saw you wrote "field.camelcase" but my answer is about "field.camelcase-underscore". The principles are the same and I guess you get the point ;)
the portion after the '.' is the so called naming strategy, that you should specify when the name you write in the hbm differ from the backing field. In the case of field.camelcase you are allowed to write CustomerName in the hbm, and NHibernate would look for a field with name customerName in the class. The reason for that is NHibernate not forcing you to choose a name convention to be compliant, NH will works with almost any naming convention.
There are cases where the properties are not suitable for NH to set values.
They may
have no setter at all
call validation on the data that is set, which is not used when loading from the database
do some other stuff that is only used when the value is changed by the business logic (eg. set other properties)
convert the value in some way, which would cause NH performing unnecessary updates.
Then you don't want NH to call the property setter. Instead of mapping the field, you still map the property, but tell NH to use the field when reading / writing the value. Roger has a good explanation why mapping the property is a good thing.
Is there any way to create an “alias” for a component?
I have a “Criteria Builder” that takes strings in the format of “Address.City” (or “User.Address.City”, …) and creates an ICriteria (filters and sorts) based on it.
I am using components to map the “Address” class so it stays in the same table as “User”.
The exception I am getting is:
NHibernate.QueryExceptioncould not resolve property: City of: MyNamespace.User
If I attempt to do not create an “alias” for the Address Component, it works just fine.
However, as it is a criteria builder, is there a way to detect that “Address” is a component and avoid the call criteria.CreateAlias(“Address”)? Any work around?
This is the same question as mine, however the solution is not viable to me (I do not create criteria manually for each query).
Any help would be much appreciated!
You can't create an Alias for Address because Address is not a mapped entity. The only difference between CreateAlias and CreateCriteria is that the former returns the original Criteria, whereas the latter returns the new Subcriteria. So the only classes you can create Criteria for are classes that have been mapped. Since components are not mapped classes, you can't create a criteria around them.
The only suggestion I have is to have your Address class either to implement an empty descriptor interface like IComponent or mark it with a custom ComponentAttribute. Then your CriteriaBuilder can check whether or not the class it's creating a criteria for has this meta data and ignore it.