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Waste of time in this forum. Bye
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It's a waste of time only because YOU made it that way by begging other people to write your code for you.
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I have a multi-layer application (user interface, business objects, data access layers). The business objects are inter-related as you might expect, so a "Group" has a property that returns an array of "Users", and each User may have multiple "Events" and each Event can have multiple "Locations" for example. Ultimately the data is accessible via a website which makes extensive use of webservices to load data dynamically. All is well and good and when a webservice loads an Event it gets all that event's Locations returned in the auto-generated JSON. When the webservice returns a Group object it also returns the list of Users, and for each User all their Events, and for each Event all the Locations. Which very quickly gets unwieldy! Not only does it make the webservice response very large, but the database is hit very hard (most of the properties are "lazy loading" so, in the rest of the application, a group's Users are loaded only when explicitly referenced, but the JSON serialization accesses ALL the properties of Group, so...)
I can control this to an extent by decorating some properties with [ScriptIgnore] (which I had to do to break some circular references; e.g. the User object has a reference to its owning Group).
However what I really need is a way to customise which properties are included depending on the context. For some webservices, all I need is the top-level object (e.g. Group), but for others I need all the Users in that group as well. Sometimes I only need a small subset of the properties of Group.
I've looked at creating very simple classes that contain just the items I need, and creating a property in the main class that populates and returns that simple class, but that seems like a lot of effort for each use case. Is there any way to use custom attributes on the properties such that I can specify an attribute name at run time and have the serializer include only matching properties?
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You can't change attributes at run-time; they're compiled into the assembly.
You can either create custom DTOs, use anonymous types, or create one or more custom JSON converters.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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Richard Deeming wrote: You can't change attributes at run-time;
yes, quite; but it's whether you can then use those attributes at run-time, as a sort of "selector" for which properties to serialise.
Using a separate DTO for each use-case seems like overkill, and having experimented with just one required much more coding than I'd like to do. It also means rebuilding the business layer DLL if I need to add in a property or create a new use-case.
I rather suspect that since there are quite a number of objects, each with a couple of different use-cases, the simplest thing (development-wise) might be to just build up the JSON response "by hand" as it were, and simply return the JSON string to the caller rather than having it built dynamically by the serializer. Then the task of adding a property or two becomes trivial and only affects the webservice methods that actually need to return them.
I'd just hoped there would be an easy way to return an object from a webservice referencing a custom attribute that would act like a "where" clause to select the properties I need... This is a personal "side" project so don't want to spend too much time on it and if a "quick and dirty" solution works, so be it...
Thanks Richard!
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As I said, an anonymous type should work:
public async Task<IActionResult> Get(int id, CancellationToken cancellationToken)
{
Group someGroup = await context.Groups.Include(g => g.Users).FirstOrDefaultAsync(g => g.Id == id, cancellationToken);
if (someGroup is null) return NotFound();
return Ok(new
{
someGroup.Id,
someGroup.Name,
someGroup.SomeOtherProperty,
Users = someGroup.Users.Select(user => new
{
user.Id,
user.Username,
user.EmailAddress,
}
});
}
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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It's an object graph (your data model); parent child relationships; you (simply) stop retrieving at the appropriate level and use empty collections for those children you don't retrieve.
That's all in the data access layer; which follows your data model.
I'm not a big fan of "giant, one line SQL / LINQ queries", and usually get superior results with chaining a number of subqueries; which makes serializing simple using one generic "object" serializer / deserializer.
"Before entering on an understanding, I have meditated for a long time, and have foreseen what might happen. It is not genius which reveals to me suddenly, secretly, what I have to say or to do in a circumstance unexpected by other people; it is reflection, it is meditation." - Napoleon I
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Thanks Gerry.Gerry Schmitz wrote: stop retrieving at the appropriate level
And therein lies the problem - how do you determine the levels to retrieve, when the object is being serialised by .Net in the webservice response processing?
In fact the way I've written it, the lower levels are only retrieved if the collection is null rather than empty. This means I could populate the object, then set the "unwanted" collections / properties to an empty object / array, before letting .Net serialise it. However that does work for non-nullable properties, which will still get serialised (with their default values) when actually I just don't want them at all. I also realised that there are some items which are confidential (e.g. user email address) and while I don't normally want that serialised, there are occasions (when invoked from an admin page and with security in the webservice itself) when I do.
I'm just a bit surprised that JSON serialisation (and by implication XML too) doesn't have a bit more dynamic control / management. That said, it's very very much simpler these days than when I first started writing AJAX applications in 2003 (before the term AJAX had been coined; I was just using raw xmlHttpRequest objects and classic ASP pages at the server...)
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Normalize your dataset. Classes will follow.
Bastard Programmer from Hell 
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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Not sure that's really a solution to this particular problem. There are use cases where I want certain related objects, and others where I don't. There are multiple combinations of multiple objects. I guess it might be possible to artificially construct classes that have the required lower levels in various combinations, but that would be bringing aspects of user interface design over into the class structure of the business layer - and in turn that affects the data access layer. Adding a further use case could result in massive amounts of rewrite. So pragmatically it's not a solution.
I'm just surprised there's not more control over serialisation!
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DerekT-P wrote: I'm just surprised there's not more control over serialisation!
That would not help you, since that's not the problem.
DerekT-P wrote: There are use cases where I want certain related objects, and others where I don't. There are multiple combinations of multiple objects. I guess it might be possible to artificially construct classes that have the required lower levels in various combinations, but that would be bringing aspects of user interface design over into the class structure of the business layer
So, you want to religouly adhere to the rules, or do as any game does and break some rules?
Bastard Programmer from Hell
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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I am very new to Asp.Net I am going to study with practical with examples so i need good and easy understanding material for my knowledge development
I am using Visual basic community 2022 and Mysql database
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C#:
Best solution is a course - if you don't understand something, then the tutor can explain in different ways until you do.
Next best is a book - Wrox, Addison Wesley, Microsoft press all do good ones which take you through the whole language, together with the framework behind it (and the framework is HUGE!)
Then there is guesswork: Think of something that might be in the language (or find a chunk of code) and try it. Kick it until it sort of does something. Ineffective and means you miss far, far too much because you don't even know they exist!
Worst of all is YouTube - most of the tutorial content is created by people who don't know how to teach, don;t know how to make a video, and generally don't know how to code. They have a chunk of code that might work, but they have no idea how it does that, and can't actually alter it to do a similar job. Remember, "Likes" and "Subscribes" make you money - and that's why the video is there. They are probably good video tutorials, but they are next to impossible to find becuas etehy are drowned in a sea of dross.
Exactly the same thing applies to MySQL: Course, Book, Guesswork, Youtube.
A C# book will cover a bit of SQL as well, when it talks about Databases - but generic SQL, rather than MySql specific. Much of it is the same, certainly the simple stuff.
Learn C# first, and get confident in your abilities there. Then learn MySql.
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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It shows record updated successfully but not updating in database
private void button13_Click(object sender, EventArgs e)
{
if (textBox6.Text != "" && textBox7.Text != "" && textBox8.Text != "")
{
string connectionString;
MySqlConnection cnn;
connectionString = @"Data Source=localhost;Initial Catalog=testDB;User ID=root;Password=mysql";
cnn = new MySqlConnection(connectionString);
//string id = Convert.ToInt32(textBox6.Text);
string id = textBox6.Text;
string name = textBox7.Text;
string salary = textBox8.Text;
textBox6.Text = "";
textBox7.Text = "";
textBox8.Text = "";
string query = "update employee set employee_id='" + this.textBox6.Text + "',employee_name='" + this.textBox7.Text + "',employee_salary='" + this.textBox8.Text + "' where employee_id='" + this.textBox6.Text + "';";
using (MySqlCommand cmd = new MySqlCommand(query))
{
cmd.Parameters.AddWithValue("@employee_id", id);
cmd.Parameters.AddWithValue("@employee_name", name);
cmd.Parameters.AddWithValue("@employee_salary", salary);
cmd.Connection = cnn;
cnn.Open();
cmd.ExecuteNonQuery();
DialogResult dr = MessageBox.Show("Are you sure to update row?", "Confirmation", MessageBoxButtons.YesNo);
if (dr == DialogResult.Yes)
{
MessageBox.Show("Record Updated Successfully");
cnn.Close();
DisplayData();
ClearData();
}
else if (dr == DialogResult.No)
{
MessageBox.Show("Dude, We keep this record as same");
}
}
}
else
{
MessageBox.Show("Please Select Record to Update");
}
}
modified 20-Mar-22 11:58am.
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Yes sir. Output came. Thanks to all
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Dude.
No.
Please burn it.
Bastard Programmer from Hell
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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I thought we discussed this ... your reply less than 5 hours ago was "Ok sir"
Is there any point in us talking to you at all?
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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if (textBox6.Text != "" && textBox7.Text != "" && textBox8.Text != "") No.
Nuke it from orbit. That's the only way to be sure.
Bastard Programmer from Hell
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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I don't think he really wants to learn - just get his homework done for him ... where he can't copy'n'paste a solution.
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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Where would one start? At textBox7, or the missing usings?
I'd burn the code and never look back.
Bastard Programmer from Hell
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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So, it's obvious you're just copying and pasting code from the web and hoping it works. You don't have any idea why there are parameter objects or how they are used in the query.
string query = "update employee set employee_id='" + this.textBox6.Text + "',employee_name='" + this.textBox7.Text + "',employee_salary='" + this.textBox8.Text + "' where employee_id='" + this.textBox6.Text + "';";
using (MySqlCommand cmd = new MySqlCommand(query))
{
cmd.Parameters.AddWithValue("@employee_id", id);
cmd.Parameters.AddWithValue("@employee_name", name);
cmd.Parameters.AddWithValue("@employee_salary", salary);
You're using the TextBox values directly in your query. NEVER DO THIS! User input should be treated like it's the spawn of Satan. Using it directly in your query will lead to SQL Injection Attacks and you risk destroying your database doing that.
Next, you NEVER change or update the value of an ID field in a table. Doing so will destroy your data integrity since records in one table will no longer relate to data in another table.
Your query should look like this (and don't even think of copying and pasting this code!) Try to figure out what the code is doing.
string query = "UPDATE employee SET employee_name=@empName, employee_salary=@empSalary WHERE employee_id=@empId";
using (MySqlCommand cmd = new MySqlCommand(query))
{
cmd.Parameters.AddWithValue("@empId", id);
cmd.Parameters.AddWithValue("@empName", name);
cmd.Parameters.AddWithValue("@empSalary", salary);
I'm ignoring that you're storing salary values as text.
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