hello i got an application that uses nhibernate as orm, i need to store data that represents time,
whats the best way to do it?
nhibenate dont know to convert time field from db to a timespan, only string.
NHibernate supports DateTime, Ticks, TimeSpan and Timestamp. Make sure you are specifying the type explicitly on your mapping element as the different time types have different semantics so what NHibernate is guessing may not be correct.
If you are and are still having problems, modify your post to include the relevant portions of your entity, mapping file, and the actual problem you are encountering.
Edit:
For example, with the following class for a TimeSpan:
public class MyClass
{
// Other properties
// ...
// ...
public virtual TimeSpan MyTimeProperty { get; set; }
}
And the mapping file:
<!-- other properties -->
<property name="MyTimeProperty" type="TimeSpan" /> <!-- Note: NH expects the DB type to be DbType.Int64 -->
You indicate that you're trying to map a TimeSpan ("nhibenate dont know to convert time field from db to a timespan, only string"). If this is the correct type matching between .NET (typeof TimeSpan) and the database (DbType.Int64), NH should do this automatically (i.e. you shouldn't need to specify type="TimeSpan"). So if it's not working, I suspect there is a problem with the way you have things setup. It may be helpful if you post the property/field declaration with full signature, the <property> line for this property from your mapping file, and the column definition from the database.
Also, make sure you use nullables for your DateTimes that can be null in database.
DateTime? instead of just DateTime.
If not, NHibernate will attempt to initialize your date to a default value which probably isn't what you want.
Related
I have POCO classes , I use NewtonSoft json for seralization. Now i want to migrate it to Google protocol buff. Is there any way i can migrate all my classes (not manually) so that i can use google protocol buff for serialization and deseralization.
Do you just want it to work? The absolute simplest way to do this would be to use protobuf-net and add [ProtoContract(ImplicitFields = ImplicitFields.AllPublic)]. What this does is tell protobuf-net to make up the field numbers, which it does by taking all the public members, sorting them alphabetically, and just counting upwards. Then you can use your type with ProtoBuf.Serializer and it should behave in the way you expect.
This is simple, but it isn't very robust. If you add, remove or rename members it can all get out of sync. The problem here is that the protocol buffers format doesn't include names - just field numbers, and it is much harder to guarantee numbers over time. If your type is likely to change, you probably want to define field numbers explicitly. For example:
[ProtoContract]
public class Foo {
[ProtoMember(1)]
public int Id {get;set;}
[ProtoMember(2)]
public List<string> Names {get;} = new List<string>();
}
One other thing to watch out for would be non-zero default values. By default protobuf-net assumes certain things about implicit default values. If you are routinely using non-zero default values without doing it very carefully, protobuf-net may misunderstand you. You can turn that off globally if you desire:
RuntimeTypeModel.Default.UseImplicitZeroDefaults = false;
Is it possible to configure NHibernate (specifically Fluent NHibernate) to serialize an array of simple types to a single database column? I seem to remember that this was possible but its been a while since I've used NHibernate.
Essentially I need to store the days of week that a person works (int[]) and would rather not have a separate table just for this purpose.
It is possible.
You need to implement a IUserType that takes care of mapping between your array and a data column (google that first; it's possible that somebody already implemented it)
Alternatively, you can do the conversion in your entity class, and map the single-field representation instead of the property. For example:
string numbers;
public int[] Numbers
{
get { return numbers.Split(','); }
set { numbers = string.Join(",", value.Select(x => x.ToString())); }
}
Yes. There's UserType for scenarios like that. You could also use enum and bit flag.
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.
I have a mapping like this
<class name="UserFileSummary" table="UserFile" lazy="false">
<id name="FileId" column="UserFileId" type="int">
<generator class="identity" />
</id>...
and a property in the c# object like this
public long FileId { get; set; }
What I don't understand is why when I get an instance using
var myFile = session.Get<UserFileSummary>(id)
change a field value and then save it like this
myFile.myProperty = newValue
session.Save(myFile)
I get an error saying the the Id have been altered from 1 to 1. There are some posts around about this, but this is a simple int column (identity 1, 1). I must have made some basic error, please can anyone help out. Thanks
I've added this bit as an edit as the question turns out to be a non question
The FileId property is type long, and the mapping is type int, that is why altered from 1 to 1 is a problem.
Please give me some feedback if you want me to delete this question, thanks everyone :)
The only thing I can point out from your code is the use of Save for updating an existing entity.
You could avoid calling explicitly the Save method for an entity that's alredy present on the session. Your changes will be automatically persisted when you flush the session.
If you insist to explicitly call the update method I'd say you should use SaveOrUpdate.
First, make the setter on the property private; the project will fail to compile if you have any code that mistakenly sets it. This is a good practice anyway. But it's not foolproof because there could be code inside the class that sets it, so you'll have to check for that.
public int FileId { get; private set; }
Second, closely examine the mapping file to make sure that you haven't mapped the field twice.
The error in my case was due to the data type being a long (int64) in the database and being mapped to an int (int32) in the mapping. This meant that the real value changed whenever the object was saved, thus breaking the identifier. Thanks to everyone who helped out.
How do you go about changing the subtype of a row in NHibernate? For example if I have a Customer entity and a subclass of TierOneCustomer, I have a case where I need to change a Customer to a TierOneCustomer but the TierOneCustomer should have the same Id (PK) as the original Customer entity.
The mapping looks something like this:
<class name="Customer" table="SiteCustomer" discriminator-value="C">
<id name="Id" column="Id" type="Int64">
<generator class="identity" />
</id>
<discriminator column="CustomerType" />
... properties snipped ...
<subclass name="TierOneCustomer" discriminator-value="P">
... more properties ...
</subclass>
</class>
I'm using the one-table per class hierarchy model, so using plain-sql, it'd be just a matter of a sql update of the discriminator (CustomerType) and set the appropriate columns relevant for the type. I can't find the solution in NHibernate, so would appreciate any pointers.
I'm also thinking whether the model is correct considering this use-case, but before I go down that route, I want to make sure doing as described above is actually possible in the first place. If not, I'll almost certainly think about changing the model.
Short answer is yes, you can change the discriminator value for the particular row(s) using native SQL.
However, I don't think NHibernate is intended to work this way, since the discriminator is generally "invisible" to the Java layer, where its value is supposed to be set initially according to the class of the persisted object and never changed.
I recommend looking into a cleaner approach. From the standpoint of the object model, you're trying to convert a superclass object into one of its subclass types while not changing the identity of its persisted instance, and that's where the conflict is (the converted object isn't really supposed to be the same thing). Two alternative approaches are:
Create a new instance of TierOneCustomer based on the information in the original Customer object, then delete the original object. If you were relying on the Customer's Primary Key for retrieval, you'll need to take note of the new PK.
or
Change your approach so the object type (discriminator) doesn't need to change. Instead of relying on a subclass to distinguish TierOneCustomer from Customer, you can use a property that you can modify freely at any time, i.e. Customer.Tier = 1.
Here are some related discussions on the Hibernate Forums that may be of interest:
Can we update the discriminator column in Hibernate
Table-per-Class Problem: Discriminator and Property
Converting a persisted instance into a subclass
You're doing something wrong.
What you are trying to do is to change the type of an object. You can't do that in .NET or in Java. That simply doesn't make sense. An object is of exactly one concrete type, and its concrete type cannot be changed from the time the object is created until the time the object is destroyed (black magic notwithstanding). In order to accomplish what you are trying to do, but with the class hierarchy you laid out, you would have to destroy the customer object which you want to turn into a tier-one customer object, create a new tier-one customer object, and copy all the relevant properties from the customer object to the tier-one customer object. That is how you do it with objects, in object-oriented languages, with your class hierarchy.
Obviously, the class hierarchy you have isn't working for you. You don't destroy customers in real life when they become tier-one customers! So don't do it with objects either. Instead, come up with a class hierarchy that makes sense, given the scenarios you need to implement. Your use scenarios include:
A customer who previously is not tier-one status now becomes tier-one status.
That means you need a class hierarchy which can accurately capture this scenario. As a hint, you should favor composition over inheritance. That means, it may be a better idea to have a property named IsTierOne, or a property named DiscountStrategy, etc., depending on what works best.
The entire purpose of NHibernate (and Hibernate for Java) is to make the database invisible. To allow you to work with objects natively, with the database magically there behind the scenes to make your objects persistent. NHibernate will let you work with the database natively, but that's not the type of scenario which NHibernate is built for.
This is REALLY late, but may be of use to the next person looking to do something similar:
While the other answers are correct that you shouldn't change the discriminator in most cases, you can do it purely within the scope of NH (no native SQL), with some clever use of mapped properties. Here's the gist of it using FluentNH:
public enum CustomerType //not sure it's needed
{
Customer,
TierOneCustomer
}
public class Customer
{
//You should be able to use the Type name instead,
//but I know this enum-based approach works
public virtual CustomerType Type
{
get {return CustomerType.Customer;}
set {} //small code smell; setter exists, no error, but it doesn't do anything.
}
...
}
public class TierOneCustomer:Customer
{
public override CustomerType Type {get {return CustomerType.TierOneCustomer;} set{}}
...
}
public class CustomerMap:ClassMap<Customer>
{
public CustomerMap()
{
...
DiscriminateSubClassesOnColumn<string>("CustomerType");
DiscriminatorValue(CustomerType.Customer.ToString());
//here's the magic; make the discriminator updatable
//"Not.Insert()" is required to prevent the discriminator column
//showing up twice in an insert statement
Map(x => x.Type).Column("CustomerType").Update().Not.Insert();
}
}
public class TierOneCustomerMap:SubclassMap<TierOneCustomer>
{
public CustomerMap()
{
//same idea, different discriminator value
...
DiscriminatorValue(CustomerType.TierOneCustomer.ToString());
...
}
}
The end result is that the discriminator value is specified for inserts, and used to determine the instantiated type on retrieval, but then if a record of a different subtype with the same Id is saved (as if the record was cloned or un-bound from the UI to a new type), the discriminator value is updated on the existing record with that ID as an object property, so that future retrievals of that type are as the new object. The setter is required on the properties because AFAIK NHibernate can't be told that a property is read-only (and thus "write-only" to the DB); in NHibernate's world, if you write something to the DB, why wouldn't you want it back?
I used this pattern recently to allow users to change the basic type of a "tour", which is in reality a set of rules governing the scheduling of the actual "tour" (a single digital "visit" to a client's on-site equipment to ensure it all works properly). While they're all "tour schedules" and need to be collectable in lists/queues etc as such, the different types of schedules require very different data and very different processing, calling for a similar data structure as the OP has. I therefore completely understand the OP's desire to treat a TierOneCustomer in a substantially different way while minimizing the effect at the data layer, so, here ya go.
If you're doing it offline (e.g. in a DB upgrade script), just use SQL and ensure consistency yourself.
If this is something you plan will happen in while the app is running, I think your requirements are wrong, just like keeping the same pointer address for a different object is wrong.
If you save the ID and use it to access the customer again (e.g. in a URL) consider making a new field that contains a token for this that will be the business key. Since it's not the ID, it's easy to create a new entity instance and copy over the token (you'll probably need to remove the token from the old one).