I have a scenario where I have a propertybag of key/values that would look something like:
Entry 1 : key="Load", value="2", type="int"
Entry 2 : key="DailyStatus", value="0", type="bool"
I am trying to figure out if it's possible with nhibernate to map these values to a single table that I can pull out at a later time into .net simple types.
I am trying to avoid creating classes to contain all of this data as it can be very repetitive and doesn't allow portions of the application to be as flexible as possible. I had considered storing it in XML or JSON, but this data has to be queried against on a pretty regular basis.
Has anyone mapped dictionaries of simple types to a table in nhibernate and pulled the data back out? I suppose mapping to a generic dictionary would work:
IDictionary<string, IDictionary<object, Type>>
I can do it by hand, but if there is a builtin way for nhibernate to accomplish it that would be easier.
How about you create a class "Triplet" with attriutes id, key, value, type and then map it to a table called whatever you want?
Related
I know this question could lead to a subjective answer, but I'd like to get an opinion from someone else.
Some background
Currently I have a class that maps a private string property to a geometry column in a PostgreSQL (PostGIS) database table along with a public string for WKT. The WKT is used by PostGIS to automatically update the geometry column, using a trigger. As I don't want to include any spatial references in my domain model, all querying is done using WKT strings and a custom spatial criterion, which wraps the WKT in a spatial PostGIS function and queries the private geometry property column reference. All of this works as expected.
The question
Since I need the column reference, I also need the property in my domainmodel, for NHibernate to map to, so I was wondering, what the best solution would be, for NHibernate to never select this property.
My current solution looks as follows with Fluent NHibernate:
Map(Reveal.Member<LocationReference>("Geometry"), "geometry")
.Generated.Always()
.ReadOnly()
.LazyLoad();
This does the trick, and when I select the entity, I won't get the property, unless I manually load it (which isn't possible through the lambda extensions). Unfortunately I would still be able to do a Criteria or HQL query for the property.
So are there any ways for me to do anything that prevents NHibernate from being able to do ever include the column in a select? Or is the above solution the only way to at least ignore the column when selecting with Query<> or QueryOver<>?
Well, I ended up removing the mapped property, because, even though it was lazy, NHibernate would sometimes load it anyway. What I did was actually a bit of a hack. I needed the alias for a property from the same class, so I used the mapping from another property and split the SqlString on '.', to get the correct alias.
All of this makes perfect sense to me, and the "workaround" is not nice, but I don't see any other way of doing it. NHibernate needs to know, what property it's dealing with, to assign proper aliases. Since I'm not mapping the property, it has no way of knowing, what alias I'm looking for.
I guess I'm doing a lot of hacking, just to avoid having to reference NHibernate.Spatial...
We are using Oracle 10g database, NHibernate, WCF and Silverlight 3.0 in our project
The situation we have is that the entities in my project have many properties. But for certain situations, like showing the options in dropdown, I only want to retrieve the list of ID and Name field for that entity. I do not want to return a list of the entire entity object as a whole as there are many columns in the table. Presently I am using two SELECT queries: one to fetch the list of IDs and second to fetch the list of Names separately. Then I join these two queries and form a Dictionary and pass it to the UI.
The concern for me is that would it be possible to achieve this in a single query itself?
One approach that I know of is to create a new class having only the ID and Name property, import it into NHiberante and then form a list of this new class and send it to the UI. I want to avoid this approach for now as there are many tables for which I have to implement this functionality and hence I will have to create many new classes and corresponding xml files.
Any sort of help would be greatly appreciated.
Here is one way to do it using the Criteria API, Projections and AliasToBean. If it's a simple non-persistent class containing Id and Name you can reuse the class. NHibernate query CreateCriteria
I've got a parent and child object. Depending on a value in the parent object changes the table for the child object. So for example if the parent object had a reference "01" then it will look in the following table "Child01" whereas if the reference was "02" then it would look in the table "Child02". All the child tables are the same as in number of columns/names/etc.
My question is that how can I tell Fluent Nhibernate or nhibernate which table to look at as each parent object is unique and can reference a number of different child tables?
I've looked at the IClassConvention in Fluent but this seems to only be called when the session is created rather than each time an object is created.
I found only two methods to do this.
Close and recreate the nhibernate session every time another dynamic table needs to be looked at. On creating the session use IClassConvention to dynamically calculate the name based on user data. I found this very intensive as its a large database and a costly operation to create the session every time.
Use POCO object for these tables with custom data access.
As statichippo stated I could use a basechild object and have multiple child object. Due to the database size and the number of dynamic table this wasn't really a valid option.
Neither of my two solutions I was particularly happy with but the POCO's seemed the best way for my problem.
NHibernate is intended to be an object relational mappers. It sounds like you're doing more of a scripting style and hoping to map your data instead of working in an OOP manner.
It sounds like you have the makings of an class hierarchy though. What it sounds like you're trying to create in your code (and then map accordingly) is a hierarchy of different kinds of children:
BaseChild
--> SmartChild
--> DumbChild
Each child is either smart or dumb, but since they all have a FirstName, LastName, Age, etc, they all are instances of the BaseChild class which defines these. The only differences might be that the SmartChild has an IQ and the DumbChild has a FavoriteFootballTeam (this is just an example, no offense to anyone of course ;).
NHibernate will let you map this sort of relationship in many ways. There could be 1 table that encompasses all classes or (what it sounds like you want in your case), one table per class.
Did I understand the issue/what you're looking for?
I have a table in database which has some columns like year,name and also 12 columns (m1,m2,...,m12) representing months. I would like to map this table into one class using NHibernate, ideally, these 12 mapped columns would look like:
_mappedMonths[] = new double[12];
Has anyone a solution for this ?
If you really want to map the columns directly to an array, as you describe, take a look at the ICompositeUserType interface. You can find an article about custom NHibernate mapping here, and this blog post might be of interest as well.
However, if it is not super important you might consider mapping the columns just as you normally would, but as private/protected properties, and then create a public property in your class that exposes those private/public properties as an array. That would be a simpler and faster solution, but would result in code that is not quite as clean.
I'm not sure how to explain this. So here goes...
I'm trying to fit the method for lazy loading blobs as described here but I'm stuck with only one table.
I have a schema (fixed, in a legacy system) which looks something like this:
MyTable
ID int
Name char(50)
image byte
This is on Informix, and the byte column is a simple large object. Now normally I would query the table with "SELECT ID, Name, (image is not null) as imageexists..." and handle the blob load later.
I can construct my object model to have two different classes (and thus two different map definitions) to handle the relationship, but how can I "fool" nhibernate into using the same table to show this one-to-one relationship?
Short answer: you can't.
You either need to map it twice or (my preference) create a DTO that has the fields you want. In HQL you'd do something like:
select new MyTableDTO(t.ID, t.name) from MyTable t