I need to implement an import export module for three database tables which are internally related with primary key/foreign key constraints.
I can do both part easily using c#/linq to xml/linq to sql. Problem is, when i am importing the exported data, in database, primary key tables' id are regenerating without taking/assign the id from xml file(its natural for auto increment). For this, other tables data can't be imported/showing error that primary key constraint violates.
My goal is to import all data and keep the primary/foreign key intact.
Now, can anyone please suggest me what I can do to solve this issue please? Thanks in advance.
You can use identity insert to specify a value for identity columns.
If you specify explicit values for identity columns, you yourself are responsible for resolving conflicts. If the database already has a row with id = 1, you have to decide what to do if the import also contains id = 1: SQL Server will just throw an error.
We always used BCP operations for such tasks.
I would suggest to not make your autoincrement the primary key but to have a separate primary key which can be defined somehow else... then you won't have the problem with the autoincrement
If you don't need the ids in the XML and SQL to match (only the relationships) you could use SCOPE_IDENTITY() and maintain mapping from XML ids to SQL ids to insert properly foreign key columns in other tables.
Related
I need some functionality in my project and I don't know if its possible.
Here is a pic with the relations:
I need to update the keys relation table LessonByFacultyMember and the same keys in Scheduling table.
I mean the keys LessonNumber,LessonCoursenumber,FacultyMemberId (LessonByFacultyMember table)
and LessonNumber,CourseNumber,FacultyMemberId (Scheduling Table).
Is it possible to update this kind of relations?
UPDATE:
I just want to be clear that i mean the possibility to change the VALUE that stored in the keys dynamically in some method.
Yes you can do so by selecting Update Cascade option in Foreign key in the database.This options automatically updates the key values in the other tables. But in your case this is not needed. The table LessonByFacultyMember should have a column LessonByFacultyMemberId as a primary key and that should be in the Scheduling table as a Reference instead of putting all the three columns in the Scheduling table. If you do so ,you don't need to worry about the updating LessonNumber,CourseNumber,FacultyMemberId in the Scheduling Table. Also in your Scheduling table there should be a column SchedulingID as a Primary Key. You can take LessonByFacultyMemberId ,SchedulingID as an auto incremented integer. Also there is no need to make LessonNumber,CourseNumber,FacultyMemberId as a Primary key in the LessonByFacultyMember table. Instead you need to make them as unique key. Similarly in Scheduling table make the current primary key as unique key and have SchedulingId as primary key. In case of showing records you need to make select statement using joins and it is better to create a view for such statement. In case if still it is not clear , create a sqlFiddle on http://sqlfiddle.com/ for your schema and share that in your question or comment to this answer. I will update the same.
Is there a way of editing the primary key in MVC3 if the table only contains a primary key field. For example I have a console table and within it i have the console name as the Primary key and I want to be able to edit it and change it and save the edited value.
If there is any more info you require please let me know.
As a general rule, you should never edit primary keys. The primary key in SQL Server typically has a clustered unique index on it, so editing the primary key means you potentially have to rebuild your indexes (maybe not every time, but depending on the skew).
Instead I would create a fake primary key, such as an IDENTITY column in SQL Server, and put a UNIQUE constraint on the Name column. If your table grows large, retrieving items on an int column will also be faster than retrieving on a varchar() column.
Update:
Since I was told I didn't answer the question (even though this is the accepted answer), it is possible to change the primary key values in SQL Server. But it is not technically an edit operation, since referential integrity may prevent a true edit (I haven't tried, so feel free to conduct your own experiment!)
The operation would go something like this:
Add a new row to the primary table, using the new PK value
Run an update operation to change all FK values to the new PK value
Delete the old PK row
I'd run all that in a transaction, too. But I will state again for the record, I do not recommend taking this approach.
As aKzenT pointed out, it is best to always use an Auto-Number/Identity or Sequence (Oracle) when defining primary keys. It is much more efficient for b-tree processors to find and join numeric keys, especially when textual ones are longer that a few bytes. Smaller keys also result in fewer b-tree pages that need to be searched.
Another important reason is that auto-generated keys cannot be modified. When using modifiable textual keys, foreign keys must employ CASCADE UPDATE which many (ex. Oracle, DB2) RDBMS do not support declaratively and must be defined using triggers, which is very complicated.
In your case, replacing the textual key with an auto-generated primary key will eliminate the problem.
I'm using VS2008 to connect to a SQL server database in order to populate it in C#. It's going pretty well, I'm able to query, insert, and update all tables in my database successfully, except one. Anytime I try to query or insert into one table I get the following error:
Message = "Invalid object name 'DB_NewModelStoreContainer.DATATYPE'."
the query that generated this error is:
var test3 = (from o in context.DATATYPE
where o.DATETYPE_NAME == "Single"
select o).First();
(yes I know it should be DATATYPE, but that is not the problem =) )
Whenever I added the database to my project, for some reason it marked every attribute in the DATATYPE table as a primary key. I went into the xml of the .edmx and fixed this but I still get this error and I cannot find out why ><. Any help at all would be very greatly appreciated! Thanks in advance.
In order to work with EntityFramework ,there should be clearly mentioned PrimaryKey and Foreign Key if any exists.
If you don't have any primary Key ,make the unique column as primary key ,It should definately work. and I am wondering how could you are able to insert record without primary key
in edmx designer you might have misssed something or may be some mapping got screwed up after changes.so,modify the tables in your database to asign the primary key to every table and then try to generate the edmx from scratch.
I'm writing a quick app using LINQ to SQL to populate a db with some test data and had a problem because one of the tables had no primary key as described by this bloke Can't Update because table has no primary key.
Taking the top answer I added the IsPrimaryKey attribute to an appropriate column and the app worked even though the I haven't changed the db table itself (i.e. there is still no primary key).
I expect it will be ok for my current intentions but are there any side effects which may come from having a table without a primary key seen as having one by the LINQ object?
(I can only think it might be a problem if I tried to read from a table (or populate to a table) with data where the 'primary key' column has the same value in more than one row).
When using an ORM framework, you can simulate keys and foreign keys at ORM level, thus "hiding and overriding" the database defined ones.
That said, that's a practice that I wouldn't recommend. Even if the model is more important than the database itself, the logical structure should always match. It is ok doing what you did if you're forced to work with a legacy database and you don't have the possibility to fix it (like adding the PK on the table). But try to walk the righteous path everytime you can :)
Tables without a PK = Pure Evil.
Basically if all the table updates go through the LINQ object you should be fine. If you have a DBA that decides to modify data directly though SQL then you can quickly run into issues if he duplicates a row with the same PK value.
I'm a bit of a noob with DAO and SQL Server and I'm running into a problem when I'm trying to insert values into two tables that have a relation. The table Photos has a gpsId field which has a foreign key relation with the id field of the GPSLocations table. I want to create a new Photos entry linked to a new GPSLocation, so the code looks something like this:
gpsRow = dataset.GPSLocations.AddGPSLocationsRow("0.0N", "3.2W");
dataset.Photos.AddPhotosRow(#"c:\path\file.jpg", gpsRow);
tableAdapterManager.UpdateAll(dataset);
However this results in the following error:
A foreign key value cannot be inserted
because a corresponding primary key
value does not exist. [ Foreign key
constraint name = photoToGps ]
I'm using SQL Server CE. Is my understanding correct that the TableAdapterManager should be handling this hierarchical update? I just dragged these tables onto the XSD view and relied on its automatic creation of the wrapper classes. Do I need to change anything about the relation (eg to make it a Foreign Key constraint)? I've noticed that under some circumstances the gps id is positive and sometimes negative, is that relevant?
EDIT:
I've also ensured that the update property is set to CASCADE, which results in the same error. Hierarchical updates are set to true and there is a foreign key constraint between the two tables in the designer.
It's just the configuration of your data set. Doubleclick the relation beween the tables in the Visual Studio's dataset designer, choose Both Relation And Foreigh Key Constraint option and in the Update Rule field choose Cascade option and that must be it.
Some information about the subject is in MSDN, you can look here http://msdn.microsoft.com/en-us/library/bb629317.aspx and go to the related topics.
I've managed to track down the source of this problem, which boils down to a limitation of SQL Server CE compared with the full SQL Server. It turns out the major hint that something wasn't right was because the ids were negative. The ids are negative in the DataSet before the row is inserted into the database, at which point it gets resolved to a positive index. The fact that it wasn't becoming a positive index happened because the TableAdapterManager normally does a batch statement of INSERT followed by a SELECT to update the id. However, SQL Server CE doesn't support batch statements, so this requires extra code to be written so that we simulate the SELECT step by responding to the RowUpdated event. This MSDN article explains the steps.
Did you enable Hierarchical Updates as described here?
Is there a foreign key constraint between the two tables (there should be a line on the XSD designer connecting them)? Since your fields are named differently it might not have been automatically added when you dragged the tables to the design surface.
Since the column photoToGps (foreign key) depends on the primary key (id), you cannot add a photoToGps unless there is a corresponding id present. So what you need to is individual updates, instead of doing an UpdateAll. First update the GPSLocations table, and then the other table. That way, you will have an id existing before you add a photoToGPS for it.