I have a scenario where I want to persist document info record to a table specific to the typo of document, rather than a generic table for all records.
For example, records for Invoices will be stored in dbo.Doc_1000 and records for Receipts will be stored in dbo.Doc_2000 where 1000 and 2000 are id autogenerate and store in well-known table (dbo.TypeOfDoc.
Furthermore each dbo.Doc.xxx table have a group of system column (always the same) and could have a group of dynamic column (metadata).
Tables dbo.Doc.xxx and eventually dynamic column are clearly created at runtime.
If this is possible with NHibernate???
Thanks.
hope that I got your point. I am currently looking for a solution for a problem that looks similar. I want to integrate a feature in my application where the admin user can design an entity at runtime.
As far as I know, once the SessionFactory is configured and ready to use, there is no way to modify the mapping used by nhibernate. If you want to use a customized table structure that is configured, created and modified at runtime, you should have a place where a corresponding mapping lives, e.g. as a nhibernate mapping xml file and you have to set up a new SessionFactory each time you change the database model to reflect these changes.
Related
I’ve hit sort of a roadblock in a current project I’m working on, I don’t have a lot of web developers in my office and as a matter in fact the only other web dev just went on vacation. Anyway I was wondering if anyone could help me with structuring two of my postgres tables.
The user needs to be able to create custom data tables, one for each specific program (a parent record). The form I’ve setup for these tables allows you to add or remove inputs based on how many fields you need and then specify the name, data_type, etc.
My initial idea was to create a new table in the dB each time a user created one of these custom tables. The other web dev, who has created something similar, said it would be better to create a fields table that stores each custom field information and then have a data table that stores every cell of data tying to a field id.
I understand having the fields table so that I can retrieve just the field information and build my front-end tables and edit forms dynamically, but I’m a little confused on how to get the data into the table. I’m used to having an array of objects and each object relating to an entire row. But with this method it’s storing each cell of data instead of row of data and I don’t know the best way to select and organize it on the backend.
Data for these tables are going to be imported in from CSV files formatted to the custom table structure, below is the current structure I have for my two tables. I got a suggestion on reddit to use JSON to store each rows data, but I'm wondering how I'll be able to do sorting and filtering with this data. My current table structure is listed below, and this is before I got the suggestion to use the json data. I'm guessing if I went that route I would remove the fieldId column and instead use it for
the JSON key name, and store that fields data with it.
fields
id -- name -- program_id -- type -- required -- position -- createdAt -- updatedAt
data
id -- fieldId -- data -- createdAt -- updatedAt
So I guess my question is does this sound like the right way to structure these tables for my needs and if so can I still perform sorting and filtering on it?
I am working on a pretty straight forward C# application that uses LINQ to SQL for database access. The application is a non-web (i.e. thick client) application.
The problem that I have recently run into is with the default association name that LINQ to SQL is creating for fields that are foreign keys to another table. More specifically, I have provided an example below:
Example of Problem
The majority of my combo boxes are filled using values from a reference data table (i.e. RefData) that stores a type, description, and a few other fields. When the form initially loads, it fills the combo boxes with values based on a query by type. For example, I have a form that allows the user to add customers. On this form, there is a combo box for state. The stateComboBox is filled by running a query against the RefData table where type = stateType. Then, when the user saves the customer with a selected state the id of the RefData column for the selected state is stored in the state column of the customer table. All of this works as expected. However, if my customer table has more than one column that is a foreign key to the RefData table it quickly becomes very confusing because the association name(s) created by LINQ are Customer.RefData, Customer.RefData1, Customer.RefData2, etc... It would be much easier if I could override the name of the association so that accessing the reference data would be more like Customer.State, Customer.Country, Customer.Type, etc...
I have looked into changing this information in the DBML that is generated by VS but, my database schema is still very immature and constantly requires changes. Right now, I have been deleting the DBML every day or two to regenerate the LINQ to SQL files after making changes to the database. Is there an easy way to create these associations with meaningful names that will not be lost while I frequently re-create the DBML?
I am not sure LINQ to SQL is the best method of accessing data, period, but I find it even more problematic in your case.
Your real issue is you have the concept of your domain objects fairly static (you know what the program needs to use to get work done), but you are not sure how you are persisting the data, as your schema is in flux. This is not a good scenario for automagic updates.
If it were me, I would code the domain models so they do not change except when you desire change. I would then determine how to link to the persistent schema (database in this case). If you like a bit more automagic, then I would consider Entity Framework, as you can use code first and map to the schema as it changes.
If you find this still does not help, because your database schema changes are incompatible with the domain models, you need to get away from coding and go into a deeper planning mode. Otherwise, you are going to continue to beat your head against the proverbial wall of change.
Create a partial class definition for your Customer table and add more meaningful getter properties for the LINQ to SQL generated member names:
public partial class Customer
{
public string Name { get; set; }
[JsonIgnore]
public RefData State => this.RefData;
[JsonIgnore]
public RefData Country => this.RefData1;
}
I blogged about this here
Right now I have all my mappings as hbm.xml. I want to switch dynamically the type of Id generator for certain entities from 'identity' to 'assigned' at runtime (application start).
This is because I need to support importing data from previous system and keep existing ids.
Is this possible? How?
The generator is part of the mappings, so you need to change the mappings before creating the session factory.
This is easy to do with Fluent or ConfORM. It's possible to change XML mappings before feeding them to the configuration, but it's cumbersome.
Just check for a configuration flag (that you'll change when starting the app), and call the appropriate generator.
It's not clear why you would need to keep existing id's. I think you should not be needing to keep existing id's. Maybe you need to keep alternate id's instead?
If the previous system has it's own database, then you:
1) Need another mapping for the other table in the other database
2) Copy the data to your existing database (with key identity)
Which means you will need new id's anyway.
Example: Suppose you want to copy a table of 'airlines' and the previous system uses the 'airline-code' as the primary key. You could use an integer as primary key in your new database and the airlinecode as your alternate key.
I have a users table that is updated by other systems. I have mapped the table to my users objects and that work great. As user data is owned by another system I don't want to change the structure of that table.
I want to add metadata to the user objects, but without changing the structure of the users table. I want to add a flag that tells me whether the user is an administrator or not. I think this flag could be stored in a table that only has one column which is the id of the user. whether a matching row is present would be represented as a boolean property on the user.
Is it possible to map this in NHibernate? I would like it so that I can update this directly through NHibernate.
You should investigate the <join> mapping, usage is described in this article.
Say I'm mapping a simple object to a table that contains duplicate records and I want to allow duplicates in my code. I don't need to update/insert/delete on this table, only display the records.
Is there a way that I can put a fake (generated) ID column in my mapping file to trick NHibernate into thinking the rows are unique? Creating a composite key won't work because there could be duplicates across all of the columns.
If this isn't possible, what is the best way to get around this issue?
Thanks!
Edit: Query seemed to be the way to go
The NHibernate mapping makes the assumption that you're going to want to save changes, hence the requirement for an ID of some kind.
If you're allowed to modify the table, you could add an identity column (SQL Server naming - your database may differ) to autogenerate unique Ids - existing code should be unaffected.
If you're allowed to add to the database, but not to the table, you could try defining a view that includes a RowNumber synthetic (calculated) column, and using that as the data source to load from. Depending on your database vendor (and the products handling of views and indexes) this may face some performance issues.
The other alternative, which I've not tried, would be to map your class to a SQL query instead of a table. IIRC, NHibernate supports having named SQL queries in the mapping file, and you can use those as the "data source" instead of a table or view.
If you're data is read only one simple way we found was to wrapper the query in a view and build the entity off the view, and add a newguid() column, result is something like
SELECT NEWGUID() as ID, * FROM TABLE
ID then becomes your uniquer primary key. As stated above this is only useful for read-only views. As the ID has no relevance after the query.