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How do I Intentionally cause a database validation error on insert [closed]

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I am trying to cause a database validation error when inserting into (or editing) the database to test the try/catch
C# is too smart and catches my type casting errors.

Try inserting a value that doesn't fit into a column (a string 10 characters long in a varchar(2)),
reference a foreign key that does not exist,
a null value in a column that doesn't accept nulls,
try connecting to the database with the wrong password/user combination.
Without any sql/c# code it's hard to know how you have things setup
EDIT- answer in comments:
"do you have any identity fields? try inserting a value that already exists into that column"

I can't drop table in SQL even after tried all the methods I found on the Internet [closed]

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I can't drop an SQL table even after I tried everything I found on the web. I actually want to delete and recreate an SQL table after clicking the "SAVE" button in my C# app (a simple SQL database editor). It works fine for tables with just data (no special rules like primary keys, forbidden nulls, etc.) but for more complicated ones I call a delete function (DROP TABLE table1), then a CREATE TABLE table1 ..., it throws an error "There is already an object named 'table1' in the database". Can anyone help? Thanks in advance!

i think your issue the tables didn't drop. since there is a relationship between tables.
So if the table you doping is a FK to other table , it will not go through.
try DeleteRule = Cascade.

C# / SQL Server : MVVM insert data into multiple tables [closed]

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I work on a small project just to get to understand the mvvm model in C# better.
I work with a Microsoft SQL Server database with three tables: customer, location and address.
Every customer can have one or more locations, and every location has a specific address.
My current thought how to accomplish this:
First insert the customer.
To insert the location, get the highest customer_id and insert the location with the max(customer_id)
Then, to insert the address, get the max(location_id) and insert the address, with the location id
Is there a better way to do this?
I haven't found any tutorial with an example of inserting data into more than one table, especially not using SQL Server.
And my next problem is: what should I bind to my TextBoxes, so that I can insert the content of it?
I thought about having a save button. This button would then execute a method, where I insert the data from the bound TextBoxes. Should I do this with commands, instead of writing a method?
Thanks already!

Sql server has a OUTPUT clause which you can use
something like
INSERT INTO MyTable VALUES({CustomerName})
OUTPUT INSERTED.ID
then you can store the inserted customer's actual ID and do the rest inserts in separate queries.
As for your second question yes you should do it with Command binding to a method in your View model

The most advisable for your situation is to use a transaction.
Example.- https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqltransaction(v=vs.110).aspx

Bulk insert using AddRange in Entity framework [closed]

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I am adding multiple entities in the database using AddRange in Entity Framework:
foreach (string tagNumber in notPresent)
{
element = new TagMaster { Name = Guid.NewGuid().ToString(), IsActive = true };
element.TagCollections.Add(new TagCollection { TagNumber = tagNumber });
newTagMasters.Add(element);
}
dbContext.TagMasters.AddRange(newTagMasters);
dbContext.SaveChanges();
What I was expecting is that by adding the complete collection in context using AddRange method, there would be a single query that will be sent to database. But to my surprise, I see multiple insert statements for each record to be inserted.
Any Insights?

The problem you are running in is that sadly the entity framework commands know NO bulk inserts. Instead they generate 1 statement per line that you want to insert.
There is no workaround to this.
The only possiblity to get 1 single statement that does all the inserts is to use specific classes or libraries. As example here SqlBulkCopy which needs no external lib to be downloaded to work.
Here a link to the msdn site:
https://msdn.microsoft.com/de-de/library/system.data.sqlclient.sqlbulkcopy(v=vs.110).aspx
The usage is quite easy. You only give the constructor your connection (after opening it beforehand!) and tell it what it shall write to teh server and what the destination table name is. Then you only need to close the connection afterwards again.
sqlcon.Open();
using (SqlBulkCopy sqlBulkCopyVariable= new SqlBulkCopy(sqlcon))
{
sqlBulkCopyVariable.BulkCopyTimeout = 600; // 10 minutes timeout
sqlBulkCopyVariable.DestinationTableName = "targetTableName";
sqlBulkCopyVariable.WriteToServer(MyData);
}
sqlcon.Close();
The WriteToServer takes DataTable, DataReader or even arrays of DataRow. The exact implementation there would depend on how you want to give the data to it. So far from my personal experience: That class is quite fast and generates only 1 single statement. BUT it is only there for SqlClients. Thus if you have a different client you need to look up which class or external library would be best fitting for you.

I am afraid insertions through Linq is not optimized as you would expect. It does that by multiple insert statements as you observed. You could instead bypass Linq in those cases and use the bulk copying alternatives instead (ie: for MS SQL server use SqlBulkCopy class, for postgreSQL use Copy etc).

Whats Better: Check if table exists or always fire create statement [closed]

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Is it OK to always fire the create statements rather than checking them like
SELECT * FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_NAME = 'my_table_name'
in SQL SERVER CE and C#.
Because irrespective of the approach, there is always a single query that will be fired. Isnt it ???
I am using trasaction for creating all tables. So, I am sure if there is one table present, then definitely all of them are created.
So if i use the same transaction, then the transaction will fail right at the very first create table statement: But is this good performance wise???

Check if table exists or always fire create statement
If the table already exists in database, you will get an exception.
You can check for table existence, delete and then create it, something like:
if OBJECT_ID('dbo.my_table_name', 'U') IS NOT NULL
DROP TABLE dbo.my_table_name;
--and then
CREATE TABLE ....

If you mean try to create the table and look for an exception, then no. Exceptions are expensive, and if they are not handled properly can terminate your program unexpectedly.
The best practice would be to check for the table's existence.