We have replaced 20 tables with a consolidated table, that separates each set of data via a "set id" (all the records for table "A" have a set_id of 1, table "B" is 2, etc.).
We then built views on the table, and renamed each so they had the views had the same names as the original 20 tables, with a WHERE to add the set_id. Net result - inserts/updates/selects of the views still work
We did this so our web page, which uses a sqldatasource with "sql command builder", wouldn't have to change. We added an INSTEAD OF INSERT trigger on each view, so that when you insert into the view, it adds the set_id and inserts into the consolidated table. So far, so good.
It partially works: UPDATEs and DELETEs work, because they know the actual ID for the record.
However INSERTs don't - when the command actually executes, we see "exec sp_executesql insert into consolidatedtable" - rather than hitting the view, the data source control finds the underlying table, then inserts directly into it. If we try adding fields to the views, they then show up in the data source control, but the web page then shows a configurable field.
Is there a way to change things on the database side to force it to use the view? My only other option at this point is to replace the views with tables, add an AFTER INSERT, UPDATE, DELETE trigger so that the consolidated gets updated, and then a process to make sure they're in sync and there are no issues.
MANY thanks in advance.
Related
I have a table COMPANY where companies are kept. I want to create a view of that table, let's name it COMPANY_CDC but with one caveat:
When an entry in the original table is deleted, I want to set a deleted flag on the view entry instead of deleting it.
EDIT Why soft deletes? The point is that im performing change data capture using JDBC, and JDBC is only able to capture soft deletes. Inserts / updates are no problem.
If this cannot be done by using a view, what would be an alternative solution?
You can insert deleted values in another table using trigger
, and with join of these two table you can create your view.
I have an existing database in MS SQL server and want to rename some tables and columns because the names currently used aren't accurate to what it represents.
I have multiple web and desktop applications that access the database, using Entity Framework (code first). Too many to update in one go and cannot afford for all apps to start working.
I was thinking it was nice is SQL server allowed a 'permanent' alias for tables and columns but I don't think this feature exists.
Or I was wondering if there was a way in EF to have two names for the same property?
For the tables, you could rename them and then create a synonym with the old name pointing to the new name.
For the columns, changing their name will break your application.You could create computed columns with the old name as well, that simply display the value of the new named column though (but this seems a little silly).
Note, however, that a computed column cannot reference another computed column, so you would have to duplicate the column in its entirety. That could lead to problems down the line if you don't update the definition of both columns.
A view containing a simple select statement acts exactly like a table. You really need to fix this properly across the database and applications. However if you want to go the view route, I suggest you do this:
Say you have a table called MyTable that you rename TheTable and with a column called MyColumn that you want to rename to TheColumn
Create a schema, say, new
Move the original table into it with this ALTER SCHEMA new TRANSFER MyTable
Rename the table and column.
Now you have a table called new.TheTable with a column called TheColumn. Everything is broken
Lastly, create a view that looks just like the old table
CREATE VIEW dbo.MyTable
AS
SELECT Column1, Column2, Column3, TheColumn As MyColumn
FROM new.TheTable;
Now everything works again.
All your fixed 'new' tables are in the new schema
However now everything is extra complicated
This is basically an illustration that you should just fix it properly across the whole app one at a time with careful change management. Definitely don't complicate it with triggers
Since you are using code first with multiple web and desktop applications, you are likely managing database changes from one place through migrations and ignoring changes other places.
You can create an empty migration and add code that will change the table name and column names to what you want. The migration should then create a view that will select from that table with the original table and column names. When you apply this migration, everything should still be working as normal from all applications. There are no model changes since you didn’t touch the model classes. Inserts, updates, and deletes will still happen through the view. There is no need for potentially buggy triggers or synonyms on the table in this option.
Now that you have the table changed, you can focus on the application code. If it helps, you can add annotations over the column and table names and start refactoring the code. You need to make sure you don’t make model changes that will break the other apps. If apps ignore model changes, you can get away with adding annotations over the columns and classes on all the apps before refactoring. You can get rid of the view sooner this way.
During cdc process odi is creating two views JV$ AND JV$D even both have same structure why odi need two views if both are doing the same work.
In the next paragraphs you will see the diferences (extract from link).
The JV$ view is the view that is used in the mappings where you select the option Journalized data only. Records from the J$ table are filtered so that only the following records are returned:
Only Locked records :JRN_CONSUMED=’1’;
If the same PK appears multiple times, only the last entry for that PK (based on the JRN_DATE) is taken into account. Again the logic here is that we want to replicate values as they are currently in the source database. We are not interested in the history of intermediate values that could have existed.
An additional filter is added in the mappings at design time so that only the records for the selected subscriber are consumed from the J$ table, as we saw in figure 5.
Similarly to the JV$ view, the JV$D view joins the J$ table with the source table on the primary key. This view shows all changed records, locked or not, but applies the same filter on the JRN_DATE column so that only the last entry is taken into account when the same record has been modified multiple times since the last consumption cycle. It lists the changes for all subscribers.
I have a SQL Server as backend and use ms access as frontend.
I have two tables (persons and managers), manager is derived from persons (a 1:1 relation), thus i created a view managersFull which is basically a:
SELECT *
FROM `managers` `m`
INNER JOIN `persons` `p`
ON `m`.`id` = `p`.`id`
id in persons is autoincrementing and the primary key, id in managers is the primary key and a foreign key, referencing persons.id
now i want to be able to insert a new dataset with a form in ms access, but i can’t get it to work. no error message, no status line, nothing. the new rows aren’t inserted, and i have to press escape to cancel my changes to get back to design view in ms access.
i’m talking about a managers form and i want to be able to enter manager AND person information at the same time in a single form
my question is now: is it possible what i want to do here? if not, is there a “simple” workaround using after insert triggers or some lines of vba code?
thanks in advance
The problem is that your view is across several tables. If you access multiple tables you could update or insert in only one of them.
Please also check the MSDN for more detailed information on restrictions and on proper strategies for view updates
Assuming ODBC, some things to consider:
make sure you have a timestamp field in the person table, and that it is returned in your managers view. You also probably need the real PK of the person table in the manager view (I'm assuming your view takes the FK used for the self-join and aliases it as the ID field -- I wouldn't do that myself, as it is confusing. Instead, I'd use the real foreign key name in the managers view, and let the PK stand on its own with its real name).
try the Jet/ACE-specific DISTINCTROW predicate in your recordsource. With Jet/ACE back ends, this often makes it possible to insert into both tables when it's otherwise impossible. I don't know for certain if Jet will be smart enough to tell SQL Server to do the right thing, though.
if neither of those things works, change your form to use a recordsource based on your person table, and use a combo box based on the managers view as the control with which you edit the record to relate the person to a manager.
Ilya Kochetov pointed out that you can only update one table, but the work-around would be to apply the updates to the fields on one table and then the other. This solution assumes that the only access you have to these two tables is through this view and that you are not allowed to create a stored procedure to take care of this.
To model and maintain two related tables in access you don’t use a query or view that is a join of both tables. What you do is use a main form, and drop in a sub-form that is based on the child table. If the link master and child setting in the sub-form is set correctly, then you not need to write any code and access will insert the person’s id in the link field.
So, don’t use a joined table here. Simply use a form + sub-form setup and you be able to edit and maintain the data and the data in the related child table.
This means you base the form on the table, and not a view. And you base the sub-form on the child table. So, don't use a view here.
Huge database in mssql2005 with big codebase depending on the structure of this database.
I have about 10 similar tables they all contain either the file name or the full path to the file. The full path is always dependent on the item id so it doesn't make sense to store it in the database. Getting useful data out of these tables goes a little like this:
SELECT a.item_id
, a.filename
FROM (
SELECT id_item AS item_id
, path AS filename
FROM xMedia
UNION ALL
-- media_path has a different collation
SELECT item_id AS item_id
, (media_path COLLATE SQL_Latin1_General_CP1_CI_AS) AS filename
FROM yMedia
UNION ALL
-- fullPath contains more than just the filename
SELECT itemId AS item_id
, RIGHT(fullPath, CHARINDEX('/', REVERSE(fullPath))-1) AS filename
FROM zMedia
-- real database has over 10 of these tables
) a
I'd like to create a single view of all these tables so that new code using this data-disaster doesn't need to know about all the different media tables. I'd also like use this view for insert and update statements. Obviously old code would still rely on the tables to be up to date.
After reading the msdn page about creating views in mssql2005 I don't think a view with SCHEMABINDING would be enough.
How would I create such an updateable view?
Is this the right way to go?
Scroll down on the page you linked and you'll see a paragraph about updatable views. You can not update a view based on unions, amongst other limitations. The logic behind this is probably simple, how should Sql Server decide on what source table/view should receive the update/insert?
You can modify partitioned views, provided they satisfy certain conditions.
These conditions include having a partitioning column as a part of the primary key on each table, and having a set on non-overlapping check constraints for the partitioning column.
This seems to be not your case.
In your case, you may do either of the following:
Recreate you tables as views (with computed columns) for your legacy soft to work, and refer to the whole table from the new soft
Use INSTEAD OF triggers to update the tables.
If a view is based on multiple base tables, UPDATE statement on the view may or may not work depending on the UPDATE statement. If the UPDATE statement affects multiple base tables, SQL server throws an error. Whereas, if the UPDATE affects only one base table in the view then the UPDATE will work (Not correctly always). The insert and delete statements will always fail.
INSTEAD OF Triggers, are used to correctly UPDATE, INSERT and DELETE from a view that is based on multiple base tables. The following links has examples along with a video tutorial on the same.
INSTEAD OF INSERT Trigger
INSTEAD OF UPDATE Trigger
INSTEAD OF DELETE Trigger