Is there a way to validate a property that should be unique on a model? For example, a user can create and edit a "Product", but they shouldn't be able to create a Product with an existing ProductCode, nor should they be able to edit a Product and change the ProductCode to a code that already exists.
I have tried using a custom attribute.
public class Unique : ValidationAttribute
{
public override bool IsValid(object value)
{
var products = Repository.Store.Products.Where(x => x.ProductCode == value);
return (products.Count() == 0);
}
}
All that I can cover with this solution is not allowing the user to insert/update a Product when the code already exists in the DB. This does not allow the user to edit an existing product because when they submit, it will see that the code already exists(it will be the code for the product they are trying to edit.) and returns false.
Is there no way of dealing with a unique index in MVC 2, I have searched for hours, even found other topics on stackoverflow, but nothing with a solid solution.
Just let the insert or update fail and then return an appropriate error message to the user. Checking up front is problematic anyway since there's always a chance that another user will modify the database immediately after your check.
Here's an example of how you can insert an object and determine whether or not it failed due to a unique constraint:
INSERT INTO MyTable (column1, column2, column3)
SELECT #param1, #param2, #param3
WHERE NOT EXISTS (SELECT * FROM table WHERE id = #param4)
If the object already exists, this will modify 0 rows. If it does not, then it will modify 1 row. If anything else goes wrong, you'll get an exception. This is also quite efficient (at least in SQL server). It results in an index seek followed by an index update, just as you would hope.
I struggled with MVC a little in a related area.
Part of the answer gleaned to my question was that you should "probably" have a seperate model for Insert and Update of an object.
That way you could have your custom attribute just on the insert model.
Otherwise, just take care of this as a normal code check in your insert method, not in a custom attribute.
Ok I see....
Can you do a "does not equal" check on the exists for some unique ID on the object - that way you check for the existence of the product code BUT not on the current product.
Related
This is a bit of a puzzle I'm trying to figure out.
I am working on a system where we have a number of company records saved in the database. Some of these records are duplicates and are no longer wanted/required.
However, several external systems are still mapping to these invalid records. If we were to delete them entirely it would cause errors to the systems still wanting to get the detail of that company.
The ideal workflow I would like would be;
The external system looks up Company ID X.
The current system has a table which has a record of all the remapped records, so when the request comes in, the table specifies to redirect Company ID X to Company ID Y.
There are a number of endpoints that could be altered one-by-one to do this - but it would be time-consuming, resulting in lots of repetition too.
My question is, using Entity Framework and .Net - is there a smart way of achieving this workflow?
My initial thoughts were to do something with the constructor for the company object, which repopulates the object from EF if a 'redirect' exists, but I don't know if this will play nice with navigation properties.
Would anyone have an idea?
Thanks very much.
You can create a column with foreign key for the same table to express the single unique valid company.
For example, you can add DuplicateOf column:
ALTER TABLE [Company]
ADD COLUMN [DuplicateOf] bigint NULL,
FOREIGN KEY [DuplicateOf] REFERENCES [Company] ([Id]);
and express this relation in your code:
public class Company
{
// ...
public Company DuplicateOf { get; set; }
// May be useful, hides check for duplicate logic:
public bool IsDuplicate => DuplicateOf != null;
// May be useful as well,
// returns the non-duplicate uniue company, not a duplicate, either linked or current:
public Company EffectiveCompany => DuplicateOf ?? this;
}
You will have to address EffectiveCompany when you want to work with non-duplicate and maintain this column to always point to the correct record. It will also result into additional query, if eager-loaded.
Another idea is to have a stored procedure GetCompany(bigint id) which will return the effective record - if DuplicateOf exists, or record itself otherwise. It will be good for your external systems and will let you hide all this stuff behind abstraction layer of stored procedure. If you decide to change it in future, then you can easily update it without breaking external systems.
However, for you it isn't always convenient to work with stored procedures with EF.
These are just ideas and not the best solutions, anyway.
In my opinion, the best solution would be to get rid of duplicates, update data everywhere and forget forever about this mess of duplicated data.
I have a table and it has one of the attribute set as identity. I want to get the value of the identity attribute that would be generated after I enter a value to the database.
I have EmpTable made of EmpID and EmpName. EmpID is set as Identity. I want to fetch the EmpID value before inserting a new row to the database.
I would advise against trying to do this with a table that is set up to use an integer column as the primary key. You will run into concurrency problems if you simply fetch the previous ID and increment it. Instead you should use a GUID (uniqueidentifier in SQL) as your primary key.
This will allow you to generate a new GUID in your code that can safely be saved to the database at a later stage.
http://msdn.microsoft.com/en-us/library/system.guid.newguid.aspx
http://msdn.microsoft.com/en-us/library/ms187942.aspx
Sure the server knows where the auto-increment count is in its sequence, but there is almost nothing useful you can do with that information. Imagine you go to the Post Office and they hand out numbered tickets so they can serve customers in order. Of course you could ask them what the next number they'll give out is, but since anyone can walk in at any time you don't know you'll get that number. If you don't know that you'll get it, you can't do anything with it - e.g. writing it as a reference number on a form would be a mistake.
Depending on what you're trying to do, your two main options are:
Use a client-generated guid as your identifier. This kind of messes up the order so the analogy isn't great, but imagine if each customer who walked in could generate a random number that they are sure would never have been used before. They could use that to fill out forms before taking a number.
Take a number, but do it in a transaction with the other operations. A customer can take a number and use it to fill out some paperwork. If they realize they left their money at home, they just throw everything away and you never call their number.
Why do you think you need this information? Can you use either of these strategies instead?
i want to set a property value in a table to default auto increment,but their are no options to do so in lightswitch2012 to my knowledge which is given that i recently started learning lightswitch,very light.
ok heres the real problem,this is the table
[customer][id,customer_id,name]
i want to set customer_id by default to id unless it is manually changed to different value.
how to acheive this?
In the Entity designer make your Customer_ID not required.
Write Code for Customers_Inserted.
Then, check to see if the Customer_ID is null. If it is, copy the ID field to it.
private void Customers_Inserted(Customer entity)
{
if (entity.Customer_ID == null) {
entity.Customer_ID = entity.ID;
}
}
You're right, there is no "auto-increment" data type available in LightSwitch. The ID property auto-increments, but that's a special case, handled by LightSwitch.
If you were attaching to an external SQL database, if you added a column that was an Integer Identity column, although it'll just appear as an Integer property in LightSwitch, it would still auto-increment because that's actually done in the SQL database itself.
The problem with all auto-increment properties is that you won't get the actual value until the record is saved.
Can I ask why you need an auto-increment property?
I may be misunderstanding what you are trying to achieve, but if you are using either a table or a grid, and you want to set the values for various entities for each new row your user adds (like customer_id = id, etc.), you can use the _Changed method and Add event to programmatically set any of the new row entities.
If this is along the lines of what you're looking for, watch Beth Massi's video How Do I: Copy Data from One Row into a New Row? You should be able to adapt her code to accomplish what you have in mind I think.
I'm creating a database where users can enter some Error Reports and we can view them. I'm making these database with C# in the ASP MVC 3 .NET framework (as the tags imply). Each Error Report has a unique ID, dubbed ReportId, thus none of them are stored under the same Id. However, whenever a User creates a new Error, I pass their User Name and store it in with the rest of the report (I use User.Identity.Name.ToString() to get their name and store it as a string). I know how to get a single item from the data using a lambda expression, like so:
db.DBSetName.Single(g => g.Name == genre)
The above code is based on an MVC 3 tutorial (The Movie Store one) provided by ASP. This was how they taught me how to do it.
My major question is: is there a member function like the .Single one that will parse through the whole database and only output database entries whose stored User Name matches that of the currently logged in user's? Then, I can use this to restrict User's to being only able to edit their own entries, since only their entries would be passed to the User's View.
What would be the best way to implement this? Since the ReportId will not be changed, a new data structure can be created to store the user's Errors and passed through to the Index (or Home) View of that particular controller. From there they should be able to click any edit link, which will pass the stored ReportId back to the Edit Action of this particular controller, which can then search the entire database for it. Am I right in assuming this would work? And would this be ideal, given that the other items in the database are NOT passed through to the Index in this method, meaning the User does not have access to the other items' ReportId's, which the user needs to pass into the Edit Action for it to work? If this is ideal, this is the method that requires me to know how to parse through a database and grab every element that fits a particular description (stored User Name matches User's current User Name).
Or would a better approach be to pass the whole database to the Index View and only output the database entries that have User Name values that match the current logged in user's? I guess this could be done in a foreach loop with a nested if loop, like so:
#foreach(var item in db.Reports)
{
if(item.UserName == User.Identity.Name.ToString())
{
...code to output table...
}
}
But this passes the whole database which gives the user a lot more info than they need. It also gives them potential access to info I don't want them to have. However, I don't have to make a new data structure or database, which should lower server memory usage and fetch time, right? Or are databases passed by copy? If so, this method seems kinda dumb. However, I don't know if the first method would fracture the database potentially, this one certainly would not. Also don't remember if I NEED an else statement in C#, I'm more familiar with C++, where you don't need one and you also don't need {}'s for single line if's, if I need one: please don't judge me too harshly on it!
Small note: I am using CRUD Controllers made with the Entity First Framework in order to edit my database. As such, all creation, reading, updating, and deletion code has been provided for me. I have chosen not to add such basic, common code. If it is needed, I can add it. I will add what the Edit Action looks like:
public ActionResult Edit(string id)
{
Report report = db.Reports.Find(id);
return View(report);
}
It accepts a string as an id, ReportId is the id used and it IS a string. It is a randomly generated GUID string made with the GUID.NewGuid().ToString() function. I will also be doing the comparison of names with:
Model.UserName == User.Identity.Name.ToString()
Which was shown earlier. Sorry if this is too much text, I wanted to provide as much info as possible and not make anyone mad. If more info is needed, it can certainly be provided. So at the end of the post, the major question actually comes down to: which of the above two methods is best? And, if it's the first one, how do I implement something like that?
Thanks for your help!
Unless I'm completely misunderstanding you, you just want .Where()
Like this:
var reports = db.Reports.Where(r => r.genre == inputGenre);
This would get you an IEnumerable of Report, which you could then use however you wish.
Imagine an object with a field that can't have a duplicate value in the database. My first instinct was to create a unique attribute that I could apply as a data annotation to a property. This unique attribute would hit the database and check if the value already exists. This would work when executing a create method, but would fail on an update. On an update, I would get a duplicate value error for every unique field of my entity whose value I don't want to change. What would be a good way, or an established practice, to accomplish this on ASP.NET MVC 2 in a way that fits nicely with the ModelState? Passing the id of my object to the attribute validator could work by checking if the duplicate value that is found is of the same entity that I am updating but I don't know how to get that data from inside of the validator.
Please forgive me if this is a stupid question or if it is phrased incoherently. It's almost 3 in the morning and I've been coding since the morning of yesterday.
For this kind of validation, I would let the database do what it already does so well. Make sure your database has the unique constraint and let it report back an error if you violate it. You can then add the error to the model errors (with a nice friendly bit of text, rather than just plonking the SQL error).
If you are determined to perform a check yourself, you can get around the UPDATE problem by excluding the current record...
SELECT COUNT(*)
FROM myTable
WHERE myTable.UniqueValue = 'ShouldBeUnique'
AND myTable.Id <> 5
In this example, you use the id of the record you are updating to avoid checking it, which means you just check other records to see if they contain the unique value.