The scenario is that, I have 2 database tables A and B. The table B is an upgraded version of the table A. (ie It might possibly have different field names and some extra fields). I need to compare these 2 tables to inform the user about these extra fields and propose to him a mapping of the fields between the tables.
Currently I am thinking of comparing them using info like field name, data element and domain in that order.
Is there a standard way to do this? Thanks in advance.
There is no standard tool to do this - why would you want to do it this way anyway? The canonical way is to extend the original table and fill the new fields in place.
Related
I am trying to figure out what the best way to design this database would be. Currently what I have works, but it requires me to hard-code values where I would like it to be dynamic in the future.
Here is my current database design:
As you can see, for both the Qualities and the PressSettingsSet tables, there are many columns that are hard-coded such as BlownInsert, Blowout, Temperature1, Temperature2, etc.
What I am trying to accomplish is to have these be dynamic. Each job will have these same settings, but I would like to allow the users to define these settings. Would it be best to create a table with just a name field and have a one-to-one relationship to another table with a value for the field and a relation to the Job Number?
I hope this makes sense, any help is appreciated. I can make a database diagram of how I think it should work if that is more helpful to what I am trying to convey. I think that what I have in mind will work, but it just seems like it will be creating a lot of extra rows in the database, so I wanted to see if there is possibly a better way.
Would it be best to create a table with just a name field and have a one-to-one relationship to another table with a value for the field and a relation to the Job Number?
That would be the simplest - you could expand that by adding data-effective fields or de-normalize it by putting it all in one table (with just a name and value field).
Are the values for the settings different per job? If so then yes a "key" table" with the name ans a one-to-many relationship to the value per job would be best.
Ok I am very new to creating databases with Entity in mind.
I have a Master table which is going to have:
departmentID
functionID
processID
procedureID
Each of those ID's need to point to a specific list of information. Which is name, description and owner of course they link back to each ID in the master table.
My question is, should I make 4 separate tables or create one table since the information is the same in all the tables except one.
The procedureID will actually need to have an extra field for documentID to point to a specific document.
Is it possible and a good idea to make one table and add some inheritance, or is it better to make 4 separate tables?
Splitting data into a number of related tables brings many advantages over one single table. Also by having data held in separate tables, it is simple to add records that are not yet needed but may be in the future. You can also create your corresponding objects for each table in your code. Also it would be more difficult to split the data into separate tables in the future if somehow you need to do that.
It might be a stupid question, but here goes:
Is it possible to make a dynamic table that's able to contain rows with variable number of columns and custom column names?
I have glanced over EAV-modelling, but it seems heavy. A real life example could be this:
Let's say I have a register with customers. But each customer might have different information to be entered. And depending on what you want to enter, it should be reflected in the database. (I.E. every customer has different columns)
Is this impossible/probable?
Update:
The standard approach (i.e. having a table with all needed columns and saving information only into columns that make sense for a particular customer while setting the remaining ones to NULL) doesn't work for me because what I want can't use 'fixed' column names. Example one customer might want CVR-number and another might want their phonenumber as a reference number. And a third might want some completely different information. So to avoid having a table containing 500 columns, I have now thought of making an extra table containing rows of column-data. Like so: Id, Name, Value, CustomerId. So when I want information for a customer, all I have to do is to iterate through this table with a specific customer Id.
my own edit!:
Sorry for troubling you with this simple SQL-issue! :-) Have a nice day...
You could model this as a one-to-many relationship between a Customer and a CustomerAttributes table. Something like:
**Customer table**
CustomerId
LastName
FirstName
...
**CustomerAttributes table**
CustomerId
AttributeName
AttributeValue
This is not possible in Sql-Server. As Marco says, you can store each customer's data in xml.
If all the columns are known ahead of time and some customers use one set and other customers use a different set, then sub-tables with each set of columns is the normal approach.
If the columns are not known ahead of time, then how would the data even be used? No code or reports could refer to it. Perhaps it should be stored unstructured in a general purpose 'Notes' field.
As far as I know it's not possible in standard relational databases, but you can take a look at schema-less databases called 'No-SQL' like MongoDB
My application has one table called 'events' and each event has approx 30 standard fields, but also user defined fields that could be any name or type, in an 'eventdata' table. Users can define these event data tables, by specifying x number of fields (either text/double/datetime/boolean) and the names of these fields. This 'eventdata' (table) can be different for each 'event'.
My current approach is to create a lookup table for the definitions. So if i need to query all 'event' and 'eventdata' per record, i do so in a M-D relaitionship using two queries (i.e. select * from events, then for each record in 'events', select * from 'some table').
Is there a better approach to doing this? I have implemented this so far, but most of my queries require two distinct calls to the DB - i cannot simply join my master 'events' table with different 'eventdata' tables for each record in in 'events'.
I guess my main question is: can i join my master table with different detail tables for each record?
E.g.
SELECT E.*, E.Tablename
FROM events E
LEFT JOIN 'E.tablename' T ON E._ID = T.ID
If not, is there a better way to design my database considering i have no idea on how many user defined fields there may be and what type they will be.
There are four ways of handling this.
Add several additional fields named "Custom1", "Custom2", "Custom3", etc. These should have a datatype of varchar(?) or similiar
Add a field to hold the unstructured data (like an XML column).
Create a table of name /value pairs which are associated with some type of template. Let them manage the template. You'll have to use pivot tables or similiar to get the data out.
Use a database like MongoDB or another NoSql style product to store this.
The above said, The first one has the advantage of being fast but limits the number of custom fields to the number you defined. Older main frame type applications work this way. SalesForce CRM used to.
The second option means that each record can have it's own custom fields. However, depending on your database there are definite challenges here. Tried this, don't recommend it.
The third one is generally harder to code for but allows for extreme flexibility. SalesForce and other applications have gone this route; including a couple I'm responsible for. The downside is that Microsoft apparently acquired a patent on doing things this way and is in the process of suing a few companies over it. Personally, I think that's bullcrap; but whatever. Point is, use at your own risk.
The fourth option is interesting. We've played with it a bit and the performance is great while coding is pretty darn simple. This might be your best bet for the unstructured data.
Those type of joins won't work because you will need to pivot the eventdata table to make it columns instead of rows. Therefore it depends on which database technology you are using.
Here is an example with MySQL: How to pivot a MySQL entity-attribute-value schema
My approach would be to avoid using a different table for each event, if that's possible.
I would use something like:
Event (EventId, ..., ...)
EventColumnType (EventColumnTypeId, EventTypeId, ColumnName)
EventColumnData (EventColumnTypeId, Data)
You are them limited to the type of data you can store (everything would have to be strings, for example), but you the number of events and columns are unrestricted.
What I'm getting from your description is you have an event table, and then a separate EventData table for each and every event.
Rather than that, why not have a single EventCustomFields table that contains a foreign key to the event table, a field Name (event+field being the PK) and a field value.
Sure it's not the best. You'd be stuck serializing the value or storing everything as a string. And you'd still be stuck doing two queries, one for the event table and one to get it's custom fields, but at least you wouldn't have a new table for every event in the system (yuck x10)
Another, (arguably worse) option is to serialize the custom fields into a single column of the and then deserialize when you need. So your query would be something like
Select E.*, C.*
From events E, customFields C
Where E.ID = C.ID
Is it possible to just impose a limit on your users? I know the tables underneath Sharepoint 2007 had a bunch of columns for custom data that were just named like CustomString1, CustomDate2, etc. That may end up easier than some of the approaches above, where everything is in one column (though that's an approach I've taken as well), and I would think it would scale up better.
The answer to your main question is: no. You can't have different rows in the result set with different columns. The result set is kind of like a table, so each row has to have the same columns. You can fake it with padding and dummy columns, but that's probably not much better.
You could try defining a fixed event data table, with (say) ten of each type of column. Then you'd store the usage metadata in a separate table and just read that in at system startup. The metadata would tell you that event type "foo" has a field "name" mapped to column string0 in the event data table, a field named "reporter" mapped to column string1, and a field named "reportDate" mapped to column date0. It's ugly and wastes space, but it's reasonably flexible. If you're in charge of the database, you can even define a view on the table so to the client it looks like a "normal" table. If the clients create their own tables and just stick the table name in the event record, then obviously this won't fly.
If you're really hardcore you can write a database procedure to query the table structures and serialize everything to a lilst of key/type/value tuples and return that in one long string as the last column, but that's probably not much handier than what you're doing now.
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.