there are 3 database tables (movies, reviews, users)
the reviews table include ( MemeberID, MovieID, Review Text, Rate, ReviewDate)
(the MemeberID, and MovieID in the Review are the FK of the members table and the movies table)
The Movie can have many reviews, and i'm trying to add review to a movie
even I have movie class and the member class, I have a problem, in order to insert review, i need to reference it to movie and users , link them, and i don't know how to do it
this code make a error:
" The relationship between the two objects cannot be defined because they are attached to different ObjectContext objects. "
This is my code...
public bool InsertNewReview(Movie _TheMovie, Member _TheMember, string _Text, byte _Rate, DateTime _ReviewDate)
{
Review ReviewToInsert = new Review()
{
MovieID = _TheMovie.MovieID,
MemberID = _TheMember.MemberID,
Movie = _TheMovie,
Member = _TheMember,
Rate = _Rate,
ReviewDate = _ReviewDate,
ReviewText = _Text
};
videoLib.Reviews.AddObject(ReviewToInsert);
videoLib.SaveChanges();
return true;
}
..
there are more data to insert to the Review class
Images: here
..
and the tables: (the "all columns" isn't a field in database tables)
Images: here
could you try like this
Review ReviewToInsert = videoLib.Reviews.CreateObject();
ReviewToInsert.MovieID = _TheMovie.MovieID
...
...
videoLib.Reviews.AddObject(ReviewToInsert);
videoLib.SaveChanges();
I got a solution, I need to define only the MovieID, MemberID, and not using their object
and use try & catch, to detect if thier the same MovieID (fk) and MemberID (fk) in the same row (because the review don't have is own id in the database)
public bool InsertNewReview(string _MovieID, int _MemberID, string _Text, byte _Rate, DateTime _ReviewDate)
{
try
{
Review ReviewToInsert = new Review()
{
Rate = _Rate,
ReviewDate = _ReviewDate,
ReviewText = _Text,
MovieID = _MovieID,
MemberID = _MemberID
};
videoLib.Reviews.AddObject(ReviewToInsert);
videoLib.SaveChanges();
return true;
}
catch
{
return false;
}
}
Related
I am trying to update individual records in sqlite database. I know how to Insert and delete records. I'd like to Update an individual record in a similar way to how I am deleting an individual record below. This uses a linq statement to get the record by Asset ID. I'd then like to pass my data to this to update.
I've also included how I insert a new record for reference. Does anybody have an example that they could share?
Delete an existing record
using (SQLiteConnection localconn = new SQLiteConnection(App.FilePath))
{
localconn.CreateTable<Road_Inspections>();
localconn.Table<Road_Inspections>().Where(x => x.Unique_ID == unique_ID).Delete();
}
Insert new record
Road_Inspections lri = new Road_Inspections()
{
ID = id,
Road_ID = Road_ID.Text.ToString(),
Asset_ID = Asset_ID.Text.ToString(),
Defect_Type = txtDefectType.Text.ToString(),
Response = txtResponse.Text.ToString(),
Inspection_Date = DateTime.Now,
};
using (SQLiteConnection conn = new SQLiteConnection(App.FilePath))
{
conn.CreateTable<Road_Inspections>();
int rowsAdded = conn.Insert(lri);
await DisplayAlert("Success", "Inspeciton Saved to Device", "OK");
}
You need a primary Key or Id in your object Announcement to identify your unique object in your database, for example:
[PrimaryKey, AutoIncrement]
public int Id { get; set; }
Since you want to update you have to get the original entry from the database first.
And then you can edit and update it. So, you don't need to delete it before you insert a new one.
In xamarin form you can use nuget sqlite-net-pcl to achieve this.
Please refer to the following code:
public Task<int> SaveItemAsync(TodoItem item)
{
if (item.ID != 0)
{
return Database.UpdateAsync(item);
}
else
{
return Database.InsertAsync(item);
}
}
For more details,you can check: https://learn.microsoft.com/en-us/xamarin/xamarin-forms/data-cloud/data/databases .
And there is a sample included in above document, you can check it here:https://learn.microsoft.com/en-us/samples/xamarin/xamarin-forms-samples/todo/
Just started learning Dapper. I have an ADO.NET background. Using a demo I downloaded, I can insert/delete data from a webform into a MySql table just fine. This, however, I have searched all morning on.
In retrieving a single row from the db by ID, it doesn't return a LIST<>, it seems to be just an object (using code from the demo I downloaded). The query works, I get the object back. It has the fields: "ProductID, Description and Price".
The only way I could get the values to those three fields was like this:
System.Reflection.PropertyInfo pi = Product.GetType().GetProperty("ProductID");
System.Reflection.PropertyInfo desc = Product.GetType().GetProperty("Description");
System.Reflection.PropertyInfo price = Product.GetType().GetProperty("Price");
int _ProductID = (int)(pi.GetValue(Product, null));
string _Description = (string)(desc.GetValue(Product, null));
decimal _Price = (decimal)(price.GetValue(Product, null));
This works and gets the correct values for the three fields.
I'm used to looping through DataTables, but I just think there is probably a better way to get those values.
Is this the correct way to do this or am I missing something? I did actually read documentation and mess with this all morning before asking, too.
Some of the things I looked at seem to be very complex. I thought Dapper was supposed to simplify things.
OK, Thanks Marc. It was difficult for me to see what was supposed to be in the Dapper class files and what was supposed to be in my code behind. The original demo way of getting a product by ID had the query as .FirstOrDefault();
I changed everything to return a List<> and it all worked. I'm sure my ADO.NET is showing, but this works. In Dapper class files:
public List<Product> ProductAsList(int Id)
{
return this._db.Query<Product>("SELECT * FROM Cart_product WHERE ProductID=#Id", new { Id = Id }).**ToList()**;
}
This is just getting one row that matched the ProductID.
In page codebehind:
protected void CartItemAdd(string ProductId) // passing it the selected ProductID
{
var results = cartservice.ProductAsList(Convert.ToInt32(ProductId));
// returns that one row using Dapper ProductAsList(ProductId)
int _ProductId = 0;
string Description = string.Empty;
decimal Price = 0;
// Loop through the list and get the value of each item:
foreach (Product obj in results)
{
_ProductId = obj.ProductID;
Description = obj.Description;
Price = obj.Price;
}
// Using Dapper to insert the selected product into the shopping cart (table):
String UserName = "jbanks";
cartitem = new CartItem();
cartitem.ProductID = _ProductId;
cartitem.Quantity = 1;
cartitem.Description = Description;
cartitem.Price = Price;
cartitem.Created = DateTime.Now;
cartitem.CreatedBy = UserName;
result = cartservice.AddCartItem(cartitem);
if (result)
{
lblMessage.Text = string.Empty;
lblMessage.Text = "Successfully added a cart item";
}
}
}
It does indeed look up the product from one table and insert a selected item into another table.
Thanks again!
The main Query<T> API returns an IEnumerable<T>, which often will be a List<T>; the AsList<T>() extension method can get it back to a list without a copy, but either way: they are just T, for whatever T you asked for. If you asked for Query<Product>, then: they should be Product instances:
var results = connection.Query<Product>(someSql, someArgs); // perhaps .AsList()
foreach (Product obj in results) { // "var obj" would be fine here too
// now just use obj.ProductID, obj.Description and obj.Price
}
If that didn't work: check that you used the <T> version of Query. There is a non-generic variant too, which returns dynamic. Frankly, you should almost always use the <T> version.
Note: I'm assuming that somewhere you have something like
class Product {
public int ProductID {get;set;}
public string Description {get;set;}
public decimal Price {get;set;}
}
I have an application which stores tasks and I want to add attachments to those tasks.
I have tried three different ways of doing this and don't know if any of them are correct and am looking for advice on where to go:
For example, simplified I have used a table:
+----------------------------------------------------------------------------+
| TaskID Description attachmentString |
+----------------------------------------------------------------------------+
| 1 Task1 "FileName1:::fileLocation;FileName2:::fileLocation" |
| 2 Task2 "FileName3:::fileLocation;FileName4:::fileLocation" |
+----------------------------------------------------------------------------+
This is similar to how profile data is stored in ASP.NET membership.
I have also tried:
+---------------------------+
| TaskID Description |
+---------------------------+
| 1 Task1 |
| 2 Task2 |
+---------------------------+
+------------------------------------------------------+
| AttachmentId Description Location TaskId |
+------------------------------------------------------+
| 1 FileName1 FileLocation 1 |
| 2 FileName2 FileLocation 1 |
+------------------------------------------------------+
If I use the first option, I can just select tasks and get all the attachment data in one SQL call; but it seems cluncky to me to have to then parse the string. Its also not very "relational"
However using an attachment Id, if I want to get the attachments, I either JOIN both tables on attachmentId and then have number of attachments x number of tasks returned. I can have up to 5 attachments so for 50 tasks, it could return 250 rows of which the first columns (from the task table side of the JOIN) are repeated and this seems like a waste. Obviously I have a little more than just description in my table!!!
I have also considered just getting the task data and then just getting the attachment data separately and then joining them in my application. This returns less data than the second option, but requires two calls to the database and that seems wrong too.
I am doing this wrong? Is there a better way? Does anyone have any thoughts on the best way to do this.
I'm not very confident with SQL and maybe I have missed something huge so any pointers would be gratefully received.
The right design is obviously two tables. Having only one table violates the first normal form.
Relating to the load problem, both approaches are correct.
Joining the tables in the sql statement is what most ORM's do to eagerly load related objects. Obviously there is some network traffic overhead, but I think it is acceptable.
Executing two separate sql statements is also correct. You can send them together in one batch to SQL Server to save roundtrips. It has a disadvantage although, you need to perform the join at the client side.
So, are you willing to write more code to save some network traffic?
EDIT:
Given the following table and data:
CREATE TABLE Tasks
(
TaskId int IDENTITY(1,1) PRIMARY KEY,
TaskDescription nvarchar(500) NOT NULL
)
CREATE TABLE TaskAttachments
(
AttachmentId int IDENTITY(1,1) PRIMARY KEY,
TaskId int NOT NULL REFERENCES Tasks(TaskId),
[FileName] nvarchar(500) NOT NULL,
[FileLocation] nvarchar(500) NOT NULL
)
GO
INSERT INTO Tasks VALUES
('Task1'), ('Task2')
INSERT INTO TaskAttachments VALUES
(1, 'FileName1', 'File location 1'),
(1, 'Filename2', 'File location 2'),
(2, 'FileName3', 'File location 3'),
(2, 'Filename4', 'File location 4')
The following classes:
public class TaskAttachment
{
public int AttachmentId { get; set; }
public string FileName { get; set; }
public string FileLocation { get; set; }
}
public class AppTask
{
public int TaskId { get; set; }
public string TaskDescription { get; set; }
public List<TaskAttachment> Attachments { get; set; }
public AppTask()
{
this.Attachments = new List<TaskAttachment>();
}
}
The following class loads the tasks with its attachments by executing two select statements in one single batch:
public class DataLayer
{
private readonly SqlConnection connection;
public DataLayer(SqlConnection connection)
{
this.connection = connection;
}
public List<AppTask> GetTasks()
{
var commandText = #"
SELECT TaskId, TaskDescription FROM Tasks;
SELECT AttachmentId, TaskId, [FileName], FileLocation FROM TaskAttachments;
";
using (var cmd = new SqlCommand(commandText, connection))
using (var reader = cmd.ExecuteReader())
{
var tasks = new List<AppTask>();
while (reader.Read())
{
var task = new AppTask
{
TaskId = reader.GetInt32(0),
TaskDescription = reader.GetString(1)
};
tasks.Add(task);
}
var taskDic = tasks.ToDictionary(x => x.TaskId);
reader.NextResult();
while (reader.Read())
{
var attachment = new TaskAttachment
{
AttachmentId = reader.GetInt32(0),
TaskId = reader.GetInt32(1),
FileName = reader.GetString(2),
FileLocation = reader.GetString(3)
};
var task = taskDic[attachment.TaskId];
task.Attachments.Add(attachment);
}
return tasks;
}
}
}
You can use the above class like this:
using (var cn = new SqlConnection("Data Source=(local);Initial Catalog=Tests;Integrated Security=SSPI"))
{
var dataLayer = new DataLayer(cn);
cn.Open();
var tasks = dataLayer.GetTasks();
}
As a part of online shopping, I implemented a cart using Session.
I have implemented the Cart in the following manner :
Session[pname] = qty;
where pname is a string variable which holds the name of the product and I used that as the key. qty is an integer variable which holds the number of items of that particular product.
To display the cart items I simply used the following loop :
foreach(string keys in Session.Keys)
Through this I get the names of the products along with the associated quantity and using this I display the cart items. The problem arises when I also have a session for the user active on the same page.
Session["uname"] = user_name;
And while retrieving the keys using Session.Keys, the uname gets included which I don't want as I need only the product's names. Is there any way I can read the keys from Session[pname] without reading from Session["uname"]?
Instead of storing an object in session for each product and quantity, just store a single object (e.g. List) which contains all of your cart items.
Here is an example which you could tweak to meet your needs:
First, a simple object to store the data:
public class CartItem {
public string Name { get; set; }
public int Quantity { get; set; }
}
Then if you need to add an object to the cart list:
var cartItems = new List<CartItem>();
cartItems.Add(new CartItem() {
Name = "",
Quantity = 1
});
Session["Cart"] = cartItems;
//Need to fetch the cart items later on?
cartItems = (List<CartItem>)Session["Cart"];
Obviously this can be implemented differently and this was just a quick example.
You mentioned needing an easier fix than what Justin Helgerson said, so here's a couple of suggestions, but they feel a little quick and dirty. Justin's is probably the superior solution. I used a quick Console app to demonstrate this, so place your constants where they belong, and you obviously don't have to create a dictionary.
const string USERSESSION = "uname";
Dictionary<string, object> session = new Dictionary<string, object>();
session["item1"] = 2;
session["item2"] = 1;
session[USERSESSION] = "StackOverflowUser";
// print cart items - minus the user name session key
foreach (string key in session.Keys.Where(s => s != USERSESSION))
{
Console.WriteLine("Key: {0} Value: {1}", key, session[key]);
}
Alternatively, if you plan on there being more keys than just "uname", use the Linq Except method.
// build up except set
List<string> exceptKeys = new List<string>
{
USERSESSION
};
foreach (string key in session.Keys.Except(exceptKeys))
{
Console.WriteLine("Key: {0} Value: {1}", key, session[key]);
}
I have two tables 1) Product 2) Categories
Product table has a field called "CategoryID" and the Category table has a field called "CategoryName", ID, DateCreated, and a few others.
I want to use LINQ to SQL to query all the Product rows as well as JUST the Category.CategoryName. This query will be used in a datasource and be bound to a ListView.
I know I can use the LoadWith option with the DataContext and a join. But the problem is that I end up with all the rows from Product and Category. What I really want is all rows from Product and just the Category.CategoryName
The perfect solution would be if the LoadWith option would let you specify the fields to return but as answered here, that's not possible.
I did find one way to do it, create a custom class which has the same exact fields that I want returned. So for example
public class ProductInfo
{
public string ProdName { get; set; }
public int ProdID { get; set; }
public int CategoryID { get; set; }
public string CategoryName { get; set; }
}
but the problem is that the select statement ends up really long. for example...
var products = from p in db.Products
join c in db.Categories on p.CategoryID = c.ID
select new ProductInfo { ProdName = p.ProdName, ProdID = p.ID,
CategoryID = p.CategoryID, CategoryName = c.CategoryName }
this becomes really error prone.
So my question - is there a better way to accomplish this?
Edit/Clarification:
i should have mentioned that the REASON i need the intermediary class is because i need to be able to return the result set as a specific type, in this case ProductInfo
I think you're pretty much on the right track, but I wouldn't really worry about the intermediery class:
var products = from p in db.Products
join c in db.Categories on p.CategoryID = c.ID
select new { p.ProdName, ProdId = p.ID, p.CategoryID,
CategoryName = c.CategoryName }
You can then wire this up in the Selecting event of the LinqDataSource. Scott Guthrie talks about in the section "Performing Custom Query Projections with the Selecting Event" in his post "Using a Custom Linq Expression with the asp:LinqDataSource" control".
oh gosh, i should have mentioned that the REASON i need the intermediary class is because i need to be able to return the result set as a specific type, in this case ProductInfo
List<ProductInfo> products = (from p in db.Products
join c in db.Categories on p.CategoryID = c.ID
select new ProductInfo { ProdName = p.ProdName, ProdID = p.ID,
CategoryID = p.CategoryID, CategoryName = c.CategoryName }).ToList<ProductInfo>();