I am working on EF database first application and I have encounter the situation where delete records from a table which has no primary key.
I have no control over the database and it is not possible to add any key for the DB table.
What is the best approach I can take?
The best approach is ,you need add a primary key.
Why EF need you add a PK?
Because, PK is a only way to identity the row in the table , if not exists a PK , the table may have many same rows(if have PK,it's different,PK is unique,each row will be different),so if your want to delete or update ,which row is your target? if not exists PK ,EF couldn't know how to identity the row ,so you must have PK in the table.
If you can't add one (may be the DB is from customer, you don't have permission), you can change the mapping XML file between EF and DB,To add a relate PK Element for a unique table column.
Related
I am trying to read in table schemas from an existing database.
I am reading in all of the tables and columns on each table using the .tables and .columns command. The .columns command returns a variable PRIMARY_KEY which lets me know it is a primary key for the table.
My question is how do I know whether a column is a foreign key to another table (and which table it is a foreign key of)?
To get information about the foreign key constraints of a table, use PRAGMA foreign_key_list.
I have a table in my database.
This table has one column named A, the column is not entity or auto number, unique key or...
I created a model from my db with Entity Framework 4.1.
My code
using (var contex = new testEntities())
{
Table_1 t = new Table_1();
t.A = 1;
contex.Table_1.Add(t);
contex.SaveChanges();
}
I do not want to use the identity number or index in my table.
When I want to insert a row in it it gives me this error:
Unable to update the EntitySet 'Table_1' because it has a DefiningQuery and no
<InsertFunction> element exists in the <ModificationFunctionMapping> element to
support the current operation.
You either have to give the table a primary key (which you don't seem to want to do) or you need to provide a function to tell Entity Framework how data can be inserted into the database.
I would strongly suggest that you put a primary key on your table unless you have a very good reason for not doing this, and in all my years I can't think of many instances when I wanted a table without a primary key.
If you don't want the primary key at all, then you might find this article useful about using Stored Procs for INSERTing data into the database: http://msdn.microsoft.com/en-us/data/gg699321.aspx
I have question, how can i insert a new data into a database that the primary key and foreign key is always equal in value?
ex. i entered my name into Name table and that Name table has PK and FK. every time i insert a new data, the FK was empty. i expect that the value of FK is same as the value of PK even they have different field name.
above is my database relationship. every time i insert new data the EventsID pk(Eventstbl) wont copy to EvnetsID FK(Organizationtbl)
The referential integrity does not work as you described. It better suits functionality of the triggers. The purpose of the PK and foreign key constraint is to prevent insertion of data which is not exist in other table as PK. Therefore, if you want to copy data from Eventstbl to Organizationtbl upon inserting a new record to the former, you need to write a trigger for the insertion event of the Eventstbl. Your PK - FK constraint will work like following, when you insert new record to Organizationtbl, it will check Eventstbl table for the corresponding EventsID. If it does not exist, it will not allow you to insert new record to Organizationtbl. I hope it helps.
Well, you can use a trigger in EventsTbl, an after insert / update trigger. So this trigger could insert / update the other table you need. You can use the INSERTED table to catch the new value of the PK. I hope it helps.
I'm using ADO.NET with a strongly typed dataset in C# (.NET 3.5). I want to insert a new row to two tables which are related in an 1:n relation.
The table Attachments holds the primary key part of the relation and the table LicenseAttachments holds the foreign key part.
AttachmentsDataSet.InvoiceRow invoice; // Set to a valid row, also referenced in InvoiceAttachments
AttachmentsDataSet.AttachmentsRow attachment;
attachment = attachmentsDataSet.Attachments.AddAttachmentsRow("Name", "Description");
attachmentsDataSet.InvoiceAttachments.AddInvoiceAttachmentsRow(invoice, attachment);
Of course when I first update the InvoicesAttachments table, I'll get a foreign key violation from the SQL server, so I tried updating the Attachments table first, which will create the rows, but will remove the attachment association in the InvoiceAttachments table. Why?
How do I solve this problem?
On the relation between the tables, ensure that the "Both Relation and Foreign Key Constraint" is selected and "Update Rule" is set to "Cascade". Combined with the "Refresh the data table" option on the adapter, after you insert your parent row, the updated ID will "Cascade" down the relationships, preventing foreign key violations in your dataset. Your child tables will then be ready to properly insert into the database.
Some things to try:
When you configure the tableadapter, did you click on advanced options, and check on "refresh data table" so that it will retrieve the identity column value?
For me sometimes I either forgot to check it, or it didn't save the configuration correctly because I didn't have my table identity increment/seed set for whatever reason. Are you using identity increment on the table?
You might also consider just re-creating the adapters for those two tables.
Usually when I go back over everything I find it was something stupid on my part.
Lastly, you might consider calling update on the Primary table, then manually grab the primary key value and manually set the value when you insert the child record. If that doesn't make sense let me know and I will post code.
You need to tell your parent table's table-adapter to refresh the
data-table after update operation.
This is how you can do that.
Open the properties of ProgramUserGroupTableAdapter -> Default Select Query -> Advnaced options. and Check the option of Refresh the data table. Save the adapter now. Now when you call update on table-adapter, the data-table will be updated [refreshed] after the update operation and will reflect the latest values from database table. if the primary-key or any coloumn is set to auto-increment, the data-table will have those latest value post recent update.
Now you can Call the update as pug.Update(dsUserGroup.ProgramUserGroup);
Read latest values from the ProgramUserGroup coloumns and assign respective values into the child table before update. This will work exactly the way you want.
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Is there an easy way to add an ID (Identity(1,1) & PK) column to a table that already has data?
I have picked up a project that was freelanced out to a horrible developer that didn't put a PK, index or anything on the tables he made.
Now that I am LINQ-ifying it, I have no PK to insert or update off of.
ALTER TABLE MyTable ADD id INT IDENTITY(1,1) PRIMARY KEY CLUSTERED
I'd be tempted to do it in three stages -
Create a new table with all the same
columns, plus you primary key column
(script out the table and then alter
it to add a PK field)
Insert into the new table all of the
values from the old table
Once your happy with it, delete the
old table and rename your new one
with the Primary Key the same as the
old table.
Open up SQL Server Management Studio
Right click the table
Click Modify
Add the Column
Set the Properties ((Is Identity) Yes, Identity Seed 1, Identity Increment 1)
Right click the Column
Click Set Primary Key
Ctrl-S