Problem with Database - Foreign Key always Null (T-SQL)

Question

My problem might be a bit long to describe as the project we are working on is a bit bigger, but i will try to be as precise as i can.

Basically we're developing a web-bases woundmanagement (part of a project for university) where the user can enter wounds and set additional information like size, consistence, upload a picture, choose the location, ... . All those information should be stored in a database (we're working with MS SQL Studio and Visual Studio 2017) where the user can also retrieve it later to view it on the module.

The problem we are facing now is that if we want to show a wound to a special wound to the user, we can't get the foreign keys to work. We can filter via the casenumber (which is working) but we can't filter wound information by the ID of the wound (each wound is getting an unique ID) - so if we choose a wound, we still get information about ALL wounds which are stored for the given casenr.

This is our "main-table" where each wound is getting an unique ID which is also an ascending identity column:

    [wound_id]          INT           IDENTITY (1, 1) NOT NULL,
    [wound_type]        VARCHAR (500) NULL,
    [wound_description] VARCHAR (500) NULL,
    [decuGrade]         INT           NULL,
    [wound_comments]    VARCHAR (500) NULL,
    [wound_timeReal]    DATETIME      NULL,
    [wound_timeGiven]   DATETIME      NULL,
    [casenumber]        INT           NULL,
    [username]          VARCHAR (50)  NULL,
    PRIMARY KEY CLUSTERED ([wound_id] ASC)
);

If the user enters the information and clicks "Next", a function is called in code behind which fills the table:

 _db.SaveWoundDetails(casenr, woundValue, decu, additional_info, realTime, givenBackDocDate, user);

This leads to our database-class, where we have our queries for the database, in this case:

 public void SaveWoundDetails(int casenr, string woundType, int decuGrade, string woundComment, DateTime timeReal, DateTime timeGiven , string user)
        {
            var table = ConfigurationManager.AppSettings["woundDetailsTable"];
            var insertQuery = "INSERT INTO " + table + "(casenumber, wound_type, decuGrade, wound_comments, wound_timeReal, wound_timeGiven, username) VALUES (@casenr, @woundType, @decuGrade, @woundComment, @timeReal, @timeGiven, @user)";


            var cmd = new SqlCommand(insertQuery);

            cmd.Parameters.AddWithValue("@casenr", casenr);
            cmd.Parameters.AddWithValue("@woundType", woundType);
            cmd.Parameters.AddWithValue("@decuGrade", decuGrade);
            cmd.Parameters.AddWithValue("@woundComment", woundComment);
            cmd.Parameters.AddWithValue("@timeReal", timeReal);
            cmd.Parameters.AddWithValue("@timeGiven", timeGiven);
            cmd.Parameters.AddWithValue("@user", user);
            var db = DatabaseController.getDataBaseController();

            try
            {
                var sqlcmd = db.executeSQL(cmd);
            }
            catch (SqlException e)
            {

            }
        }

The connection etc. is in a Database-handler class which is not relevant at the moment.

Until here it works fine. But now we have a second table for more information about the wound, which is also filled on next click, related to this table:

CREATE TABLE [dbo].[epadoc_mod_wound_progress] (
    [progress_id]       INT           IDENTITY (1, 1) NOT NULL,
    [wound_length]      INT           NULL,
    [wound_width]       INT           NULL,
    [wound_depth]       INT           NULL,
    [wound_surrounding] VARCHAR (500) NULL,
    [wound_consistence] VARCHAR (500) NULL,
    [wound_state]       VARCHAR (200) NULL,
    [wound_painscale]   VARCHAR (MAX) NULL,
    [wound_itch]        VARCHAR (MAX) NULL,
    PRIMARY KEY CLUSTERED ([progress_id] ASC)

With the INSERT-METHOD:

 public void SaveWoundProgress(int woundLength, int woundWidth, int woundDepth, string woundSurrounding, string woundConsistence, string woundState, string woundPainScale, string woundItch)
        {
            var table = ConfigurationManager.AppSettings["woundProgressTable"];
            var insertQuery = "INSERT INTO " + table + "(wound_length,wound_width,wound_depth, wound_surrounding, wound_consistence, wound_state, wound_painscale, wound_itch) VALUES (@woundLength, @woundWidth, @woundDepth, @woundSurrounding, @woundConsistence, @woundState, @woundPainScale, @woundItch)";


            var cmd = new SqlCommand(insertQuery);

            cmd.Parameters.AddWithValue("@woundLength", woundLength);
            cmd.Parameters.AddWithValue("@woundWidth", woundWidth);
            cmd.Parameters.AddWithValue("@woundDepth", woundDepth);
            cmd.Parameters.AddWithValue("@woundSurrounding", woundSurrounding);
            cmd.Parameters.AddWithValue("@woundConsistence", woundConsistence);
            cmd.Parameters.AddWithValue("@woundState", woundState);
            cmd.Parameters.AddWithValue("@woundPainScale", woundPainScale);
            cmd.Parameters.AddWithValue("@woundItch", woundItch);
            var db = DatabaseController.getDataBaseController();

            try
            {
                var sqlcmd = db.executeSQL(cmd);
            }
            catch (SqlException e)
            {

            }
        }

And the method

_db.SaveWoundProgress(wound_length, wound_width, wound_depth, woundArea, woundEdge, woundStatus, painStatus, itchStatus);

which is execute right after the method mentioned above.

I know how to create foreign keys between two tables, but everything we tried failed - if we try to execute it with a foreign key set which is NOT NULL, we're getting a null-exception.

Example of what we tried:

CONSTRAINT [FK_epadoc_mod_wound_details] FOREIGN KEY ([wound_id])
REFERENCES [dbo].[epadoc_mod_wound_progress] ([progress_id])

If we set a foreign key like this, it didn't work.

We came to the conclusion that it must be a problem the callstack when the two methods are executed - but we don't know how we can fix it. Maybe we have to set the foreign key in the INSERT-query as an explicit variable?

What we want to achieve is that the wound_id of the details-table is taken as foreign key the the progress-table so that a wound can be later changed (for example if it heals the user could re-enter the new size etc.) and we can filter by ID to just show ONE wound to the patient and not all wounds at the same time if clicked on a specific wound.

Sadly i'm not the big database expert so i hope that you can follow my explanations :).

Thanks for any help!

*Remove* all those `catch{}` blocks that hide errors. Right now you don't know if any of those statements succeed or throw an error. `catch{}` doesn't remove errors or make your code more robust, it means you have no way of knowing if it even works — Panagiotis Kanavos, Feb 12 '19 at 13:59

score 3 · Accepted Answer · answered Feb 12 '19 at 14:03

3

Your epadoc_mod_wound_progress needs to include a [wound_id] INT NOT NULL column. This is what your foreign key should be built on so that one wound can have many wound progresses. Then, in your insert statement, you'll insert the wound_id that generates in woundDetail table insert into epadoc_mod_wound_progress.

answered Feb 12 '19 at 14:03

Michael

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25

Hey, first - thanks for your answer! So i have to get the id first via select statement and enter it afterwards with the INSERT? Or is there an easier way? :) – Max Kirsch Feb 12 '19 at 15:07
1

This link is your best strategy: https://stackoverflow.com/questions/18373461/execute-insert-command-and-return-inserted-id-in-sql Using executescalar with an insert returns the ID. I'd update your `SaveWoundDetails` method to return `int`. – Michael Feb 12 '19 at 17:12
Yeah i found it in the meantime, i used SCOPE_IDENTITY() to pass the ID to the other table :) - thanks for your help, it works now! :) – Max Kirsch Feb 12 '19 at 17:17

score 1 · Answer 2 · answered Feb 12 '19 at 14:06

Tried to add a comment but I don't have 50 reputation.

I assume from what I can see that you are trying to achieve a one to many relationship between the "main table" and the "epadoc_mod_wound_progress" table, is that right ?

If so, you don't seem to have a field in the "epadoc_mod_wound_progress" table that stores the wound_id, how are you trying to create a foreign key if you are not storing the wound_id ?

Suggest the Primary Key of the epadoc_mod_wound_progress table is a concatenated key of wound_id and progress_id, with wound_id also being the foreign key linking to the main table.

Olivier Jacot-Descombes · Answer 3 · 2019-02-12T14:13:47.323

In table epadoc_mod_wound_progress there must be a wound_id INT NOT NULL column acting as foreign key.

Also the constraint must be added to the foreign key table, i.e. the table on the n side of the 1 to n relation. Assuming that the name of the main table is epadoc_mod_wound_details (you did not show it):

ALTER TABLE dbo.epadoc_mod_wound_progress
ADD CONSTRAINT FK_progress_details FOREIGN KEY (wound_id)
REFERENCES dbo.epadoc_mod_wound_details (wound_id)
ON DELETE CASCADE

Also, by adding ON DELETE CASCADE the progress of a wound detail will automatically be deleted when you delete the wound detail.

Problem with Database - Foreign Key always Null (T-SQL)

3 Answers3