Concurrency violation while updating and deleting newly added rows - sql

I've been developing a CRUD application using Datasets in C# and Sql Server 2012. The project is basically an agenda wich holds information about Pokémon (name, habilities, types, image, etc).
By the few months I've been facing a problem related to concurrency violation. In other words, when I try to delete or update rows that I've just added during the same execution of the program, the concurrency exception is generated and it isn't possible to perform any other changes in the database. So I need to restart the program in order to be able to perform the changes again (Important Note: this exception only happens for the new rows added through C#).
I've been looking for a solution for this violation (without using Entity Framework or LINQ to SQL), but I couldn't find anything that I could add in the C#'s source code. Does anyone knows how to handle this? What should I implement in my source code? Is there anything to do in SQL Server that could help on it?
Here is a link to my project, a backup from the database, images of the main form and the database diagram:
http://www.mediafire.com/download.php?izkat44a0e4q8em (C# source code)
http://www.mediafire.com/download.php?rj2e118pliarae2 (Sql backup)
imageshack .us /a /img 708/38 23/pokmonform .png (Main Form)
imageshack .us /a /img 18/95 46/kantopokdexdiagram .png (Database Diagram)

I have looked on your code and it seems, that you use AcceptChanges on a datatable daKanto inconsistently. In fact you use AcceptChangesDuringUpdate, which is also fine, although I prefer to call method datatable.AcceptChanges() explictly after the update, but your way also is fine.
Anyway I have noticed, that you use AcceptChangesDuringUpdate in the method Delete_Click and Update__Click, but do not use it in the Save_Click, and also I think you should use AcceptChangesDuringFill in MainForm_Load, where you fill your datasets.
I cannot guarantee you, that it will help, but I know that uniformity of data access throughout the application reduces the risk of the unexpected data consistency errors.

Related

Write conflict: I want to always Drop Changes

I have a split database and I have duplicated front-end file to make multiple copies for different users. Every-time a change is made on one front-end form, I want the other forms in other front-ends to always drop changes. How can I trap this write conflict to always drop changes maybe through VBA if possible?
Not quite sure what you mean by "drop changes" - the frontend should never be redesigned during normal use.
You must distribute a new copy of the frontend to the users.
A smooth and proven method using a shortcut and a script is described in my article:
Deploy and update a Microsoft Access application with one click
(If you don't have an account, browse for the link: Read the full article)
Edit:
If it is the data that is updated by several users, and you update via VBA, you may study another of my articles:
Handle concurrent update conflicts in Access silently
Though simple to use, the code is a bit too much to post here. It is also on GitHub:
VBA.ConcurrencyUpdates

update old processes with the new process definition -Activiti

I have some processes that ran with old process definitions. But due to requirement change the user task data has been updated with new attributes and this process definition has been deployed. I'm aware that "SetProcessDefinitionVersionCmd" can be set to "yes" to point the processes to the new definition/version.
I would like to know how to migrate the old process data to have the newly added attributes of the user task updated in them?
There is no easy way to migrate process instance data, however, when you set the version to the new process definition the instance data will go with the migrated instance.
What you have to be careful of is to make sure you include null checks for any of the data that may not be present in the migrated process instances.
Hope this helps,
Greg
Indeed there is no easy way for migration, however depending on the differences between the two definitions and to what extend you may not prefer to use SetProcessDefinitionVersionCmd, you may find DynamicBpmnService useful when combined with detecting definitions' versions inside your logic.
And yes another way would be to use SetProcessDefinitionVersionCmd but be extra cautions for tasks that were actually active prior to migration, as Activiti's database model have some redundant data (some for performance reasons), you are better studying the DB tables first for these tasks and then inspecting the before and after migration state. For example, keeping up with a simple changed attribute is much easier than an added boundary event on an active User Task, which affects the "execution tree".
I would also advice to compare SetProcessDefinitionVersionCmd's implementations between Activiti and Camunda, it is sad to have such enhancements efforts separated, but that is another story.

Exclude versioned documents while Querying-Raven db

I have appended the versioning bundle in midway of my project after having written most of my raven queries in my data access layer. Now because of versioning i have lots of replicated data. Whenever i query a type of document i can see the values replicated as many times as the document is versioned. Is there way to stop querying the re-visioned documents when i query for the current data in common without re-writing all of my queries with Exclude("Revisions").Is there any setting where i can say query on re-visioned document =False which i can set globally? please suggest something to overcome this..
That is the way it works, actually. It appears that you have disabled the versionning bundle, which would cause this to happen.

How to change specific system entities on Crm 2011?

I'm trying to change some system entities and I realize that on some system entities you cannot change anything.
For example, I can add fields and relationships on a "serviceactivity" bit it's not possible to change something in "service" or "site".
I really can't understand, why for example the "site" entity has about 20 fields which are predefined and are not used (on the form, by default) or can't even added to the form.
Is there any supported / unsupported way where i can change (add fields, relationships) to records from "site" entities?
I'm developing on Crm 2011 rollup 6.
Regards
Sebastian
I don't think you are going to find any supported way to modify the Site entity as it appears to be one of the few that Microsoft has locked down, probably due to some internal limitations that prevent other functionality from breaking. I attempted to add the Site entity to an unmanaged solution, once I exported it I was able to modify the XML directly and reimport it. CRM however appears to ignore any changes that are made. With that said I'm thinking that going down the unsupported route would likely end up breaking something later on.

Do you put your database static data into source-control ? How?

I'm using SQL-Server 2008 with Visual Studio Database Edition.
With this setup, keeping your schema in sync is very easy. Basically, there's a 'compare schema' tool that allow me to sync the schema of two databases and/or a database schema with a source-controlled creation script folder.
However, the situation is less clear when it comes to data, which can be of three different kind :
static data referenced in the code. typical example : my users can change their setting, and their configuration is stored on the server. However, there's a system-wide default value for each setting that is used in case the user didn't override it. The table containing those default settings grows as more options are added to the program. This means that when a new feature/option is checked in, the system-wide default setting is usually created in the database as well.
static data. eg. a product list populating a dropdown list. The program doesn't rely on the existence of a specific product in the list to work. This can be for example a list of unicode-encoded products that should be deployed in production when the new "unicode version" of the program is deployed.
other data, ie everything else (logs, user accounts, user data, etc.)
It seems obvious to me that my third item shouldn't be source-controlled (of course, it should be backuped on a regular basis)
But regarding the static data, I'm wondering what to do.
Should I append the insert scripts to the creation scripts? or maybe use separate scripts?
How do I (as a developer) warn the people doing the deployment that they should execute an insert statement ?
Should I differentiate my two kind of data? (the first one being usually created by a dev, while the second one is usually created by a non-dev)
How do you manage your DB static data ?
I have explained the technique I used in my blog Version Control and Your Database. I use database metadata (in this case SQL Server extended properties) to store the deployed application version. I only have scripts that upgrade from version to version. At startup the application reads the deployed version from the database metadata (lack of metadata is interpreted as version 0, ie. nothing is yet deployed). For each version there is an application function that upgrades to the next version. Usually this function runs an internal resource T-SQL script that does the upgrade, but it can be something else, like deploying a CLR assembly in the database.
There is no script to deploy the 'current' database schema. New installments iterate trough all intermediate versions, from version 1 to current version.
There are several advantages I enjoy by this technique:
Is easy for me to test a new version. I have a backup of the previous version, I apply the upgrade script, then I can revert to the previous version, change the script, try again, until I'm happy with the result.
My application can be deployed on top of any previous version. Various clients have various deployed version. When they upgrade, my application supports upgrade from any previous version.
There is no difference between a fresh install and an upgrade, it runs the same code, so I have fewer code paths to maintain and test.
There is no difference between DML and DDL changes (your original question). they all treated the same way, as script run to change from one version to next. When I need to make a change like you describe (change a default), I actually increase the schema version even if no other DDL change occurs. So at version 5.1 the default was 'foo', in 5.2 the default is 'bar' and that is the only difference between the two versions, and the 'upgrade' step is simply an UPDATE statement (followed of course by the version metadata change, ie. sp_updateextendedproperty).
All changes are in source control, part of the application sources (T-SQL scripts mostly).
I can easily get to any previous schema version, eg. to repro a customer complaint, simply by running the upgrade sequence and stopping at the version I'm interested in.
This approach saved my skin a number of times and I'm a true believer now. There is only one disadvantage: there is no obvious place to look in source to find 'what is the current form of procedure foo?'. Because the latest version of foo might have been upgraded 2 or 3 versions ago and it wasn't changed since, I need to look at the upgrade script for that version. I usually resort to just looking into the database and see what's in there, rather than searching through the upgrade scripts.
One final note: this is actually not my invention. This is modeled exactly after how SQL Server itself upgrades the database metadata (mssqlsystemresource).
If you are changing the static data (adding a new item to the table that is used to generate a drop-down list) then the insert should be in source control and deployed with the rest of the code. This is especially true if the insert is needed for the rest of the code to work. Otherwise, this step may be forgotten when the code is deployed and not so nice things happen.
If static data comes from another source (such as an import of the current airport codes in the US), then you may simply need to run an already documented import process. The import process itself should be in source control (we do this with all our SSIS packages), but the data need not be.
Here at Red Gate we recently added a feature to SQL Data Compare allowing static data to be stored as DML (one .sql file for each table) alongside the schema DDL that is currently supported by SQL Compare.
To understand how this works, here is a diagram that explains how it works.
The idea is that when you want to push changes to your target server, you do a comparison using the scripts as the source data source, which generates the necessary DML synchronization script to update the target. This means you don't have to assume that the target is being recreated from scratch each time. In time we hope to support static data in our upcoming SQL Source Control tool.
David Atkinson, Product Manager, Red Gate Software
I have come across this when developing CMS systems.
I went with appending the static data (the stuff referenced in the code) to the database creation scripts, then a separate script to add in any 'initialisation data' (like countries, initial product population etc).
For the first two steps, you could consider using an intermediate format (ie XML) for the data, then using a home grown tool, or something like CodeSmith to generate the SQL, and possible source files as well, if (for example) you have lookup tables which relate to enumerations used in the code - this helps enforce consistency.
This has another benefit that if the schema changes, in many cases you don't have to regenerate all your INSERT statements - you just change the tool.
I really like your distinction of the three types of data.
I agree for the third.
In our application, we try to avoid putting in the database the first, because it is duplicated (as it has to be in the code, the database is a duplicate). A secondary benefice is that we need no join or query to get access to that value from the code, so this speed things up.
If there is additional information that we would like to have in the database, for example if it can be changed per customer site, we separate the two. Other tables can still reference that data (either by index ex: 0, 1, 2, 3 or by code ex: EMPTY, SIMPLE, DOUBLE, ALL).
For the second, the scripts should be in source-control. We separate them from the structure (I think they typically are replaced as time goes, while the structures keeps adding deltas).
How do I (as a developer) warn the people doing the deployment that they should execute an insert statement ?
We have a complete procedure for that, and a readme coming with each release, with scripts and so on...
First off, I have never used Visual Studio Database Edition. You are blessed (or cursed) with whatever tools this utility gives you. Hopefully that includes a lot of flexibility.
I don't know that I'd make that big a difference between your type 1 and type 2 static data. Both are sets of data that are defined once and then never updated, barring subsequent releases and updates, right? In which case the main difference is in how or why the data is as it is, and not so much in how it is stored or initialized. (Unless the data is environment-specific, as in "A" for development, "B" for Production. This would be "type 4" data, and I shall cheerfully ignore it in this post, because I've solved it useing SQLCMD variables and they give me a headache.)
First, I would make a script to create all the tables in the database--preferably only one script, otherwise you can have a LOT of scripts lying about (and find-and-replace when renaming columns becomes very awkward). Then, I would make a script to populate the static data in these tables. This script could be appended to the end of the table script, or made it's own script, or even made one script per table, a good idea if you have hundreds or thousands of rows to load. (Some folks make a csv file and then issue a BULK INSERT on it, but I'd avoid that is it just gives you two files and a complex process [configuring drive mappings on deployment] to manage.)
The key thing to remember is that data (as stored in databases) can and will change over time. Rarely (if ever!) will you have the luxury of deleting your Production database and replacing it with a fresh, shiny, new one devoid of all that crufty data from the past umpteen years. Databases are all about changes over time, and that's where scripts come into their own. You start with the scripts to create the database, and then over time you add scripts that modify the database as changes come along -- and this applies to your static data (of any type) as well.
(Ultimately, my methodology is analogous to accounting: you have accounts, and as changes come in you adjust the accounts with journal entries. If you find you made a mistake, you never go back and modify your entries, you just make a subsequent entries to reverse and fix them. It's only an analogy, but the logic is sound.)
The solution I use is to have create and change scripts in source control, coupled with version information stored in the database.
Then, I have an install wizard that can detect whether it needs to create or update the db - the update process is managed by picking appropriate scripts based on the stored version information in the database.
See this thread's answer. Static data from your first two points should be in source control, IMHO.
Edit: *new
all-in-one or a separate script? it does not really matter as long as you (dev team) agree with your deployment team. I prefer to separate files, but I still can always create all-in-one.sql from those in the proper order [Logins, Roles, Users; Tables; Views; Stored Procedures; UDFs; Static Data; (Audit Tables, Audit Triggers)]
how do you make sure they execute it: well, make it another step in your application/database deployment documentation. If you roll out application which really needs specific (new) static data in the database, then you might want to perform a DB version check in your application. and you update the DB_VERSION to your new release number as part of that script. Then your application on a start-up should check it and report an error if the new DB version is required.
dev and non-dev static data: I have never seen this case actually. More often there is real static data, which you might call "dev", which is major configuration, ISO static data etc. The other type is default lookup data, which is there for users to start with, but they might add more. The mechanism to INSERT these data might be different, because you need to ensure you do not destoy (power-)user-created data.