How to create an instance of an object with a navigation property?
In my application, I am using two classes to represent an object of Fruit and an object of Color as defined below.
public class Fruit
{
public Fruit(int fruitId, string name, Color color)
{
FruitId = fruitId;
Name = name;
Color = color;
}
public int FruitId { get; set; }
public string Name { get; set; }
public Color Color { get; set; }
}
public class Color
{
public Color(int colorId, string name, List<Fruit> fruits)
{
ColorId = colorId;
Name = name;
Fruits = fruits;
}
public int ColorId { get; set; }
public string Name { get; set; }
public List<Fruit> Fruits { get; set; }
}
When creating an instance of Fruit or Color, I get their data from a database which is rather easy, but the problem is, I don't understand how to fill up the data for either the Fruit or the Color's navigation properties...
result = some_query_result_from_database...
Fruit f = new Fruit(result["FruitId"], result["Name"], ???);
Problem:
If I replace the ??? from the above code with the following:
new Color(some_colorId, some_colorName, some_list_of_fruits)
Where can I get the some_list_of_fruits?
Update #1:
The Fruit and Color objects from above represents tables from a database, for this example I named it the same, so Fruit object has a Fruit table counterpart from the database and so does the Color object:
Table definition:
+----------+
| Fruit |
+----------+
| FruitId |
| Name |
| ColorId |
+----------+
|∞
|
|1
+----------+
| Color |
+----------+
| ColorId |
| Name |
+----------+
Table contents:
Fruits
+---------+--------+----------+
| FruitId | Name | ColorId |
+---------+--------+----------+
| 10 | Apple | 70 |
| 20 | Orange | 80 |
| 30 | Grapes | 90 |
+---------+--------+----------+
Colors
+----------+--------+
| ColorId | Name |
+----------+--------+
| 70 | Red |
| 80 | Orange |
| 90 | Violet |
+----------+--------+
Update #2:
I overlooked at SriramSakthivel's comment, I realized SriramSakthivel is also asking how I get the data for my objects. So here it is.
For my Fruit object:
string cs = some_connection_string;
MySqlConnection c = new MySqlConnection(cs);
try
{
c.Open();
string query = select_statement_to_get_fruits_from_db;
...then after that, I use MySqlDataReader to loop through the result to create fruit objects
}
For my Color object, it's just the same steps like the above commands except that on my query, I replaced it with a select statement to retrieve color data from database.
You have circular dependency and you'll not be able to construct complete objects in constructor - you'll have to fill at least one side of circular dependency later.
One option is to build up collections of "fruits" while you are creating them:
Build collection of all colors first but have lists of fruits empty (Dictionary by colorId is probably what you are looking for).
When creating fruit register the fruit in Color's list of fruits:
Sample:
public Fruit(int fruitId, string name, Color color)
{
FruitId = fruitId;
Name = name;
Color = color;
color.Fruits.Add(this);
}
You can also create colors on demand while creating fruit:
public Fruit CreateFruit(int fruitId, string fruitName, int colorId)
{
if (!colorDictionary.ContainsKey(colorId))
{
var name = ...// Somehow get color name for colorID
colorDictionary.Add(colorId,
new Color { ColorId = ColorId, Name = name, List = new List<Fruits>()});
}
return new Fruit(fruitId, fruitName, colorDictionary[colorId];
}
Related
I have this data available from the database:
|----------------|--------------|----------------|----------------|----------------|----------------|
| entity_name | provider_id | provider_name | product_id | product_name | country_name |
|----------------|--------------|----------------|----------------|----------------|----------------|
| test | 123 | Provider1 | 1 | Product1 | Russia |
|----------------|--------------|----------------|----------------|----------------|----------------|
| test | 123 | Provider1 | 2 | Product2 | Spain |
|----------------|--------------|----------------|----------------|----------------|----------------|
| test | 123 | Provider1 | 3 | Product3 | France |
|----------------|--------------|----------------|----------------|----------------|----------------|
| test | 456 | Provider2 | 3 | Product3 | France |
|----------------|--------------|----------------|----------------|----------------|----------------|
| test | 123 | Provider1 | 4 | Product4 | France |
And I have to map it to this model in C#:
public class EntityModel
{
public string EntityName { get; set; }
public List<ProviderModel> Providers { get; set; }
}
public class ProviderModel
{
public int ProviderID { get; set; }
public string ProviderName { get; set; }
public List<ProductModel> Products { get; set; }
public ProviderModel() { }
}
public class ProductModel
{
public int ProductID { get; set; }
public string ProductName { get; set; }
public string CountryName { get; set; }
public ProductModel() { }
}
So basically I have to group by providers, for every provider I have to show the products:
{
"entityName": "string",
"providers": [
{
"ProviderID": 0,
"ProviderName": "string",
"products": [
{
"productId": 0,
"productName": "string",
"countryName": "string"
}
]
}
]
}
The sp that returns the data is like this:
SELECT DISTINCT
e.entity_name
,pro.provider_id
,pro.provider_name
,p.product_id
,p.product_name
,pc.country_name
FROM provider_product_table ppt
INNER JOIN product p ON ppt.product_id = p.product_id
INNER JOIN product_parent pp on pp.product_parent_id=p.product_parent_id
INNER JOIN provider pro ON pro.provider_id = ppt.provider_id
INNER JOIN product_country pc on pc.product_id=p.product_id
INNER JOIN entity e on e.product_parent_id=pp.product_parent_id
WHERE p.product_parent_id = #product_parent_id
ORDER BY p.product_id ASC
I tried a lot of groupBy versions but I get stuck at mapping the second list, the products one.
How can I achieve this? Thank you !
let's start with saying that your database is not well-structured or not created for your need, it will be more than good if you try to seprate your data into three table (entity,provider,product) with relationship between entity and provider , and relationship between your provider and the product table.
however, maybe you are developing new feature that it was not thinking at first to make your code or even your database more extensible.
in this case i need to see your group query request (the groupby ) that you created already.
meanwhile i can imagine your need, so you have several solution.
the first one is what are you trying to do , create several query that fill your classes ,i can also imagine with Redundancy, that because there are some id who are unfortunately duplicated due to your database structure, in this case you need to use DISTINCT or INTERSECT (even if its not your need here ) .
seconds one you can deal with temporary table using the keyword INTO#tmpTable if you are using sqlserver, so basically is to crate a new tables in memory to perform your query ( those tables is what i propose above ).
try to edit your question with those query you describe.
Using WPF datagrid with MVVM structure (no code behind). I was wondering if it was possible to take a model property that normally shows up in a single column and use that to dynamically generate new columns.
Example
public Class1
{
public int Property1 { get; set; }
public string Property2 { get; set; }
public double Property3 { get; set; }
}
Mock up standard datagrid
|Property1|Property2|Property3|
| 1 | A | 1.25 |
| 2 | B | 2 |
| 3 | B | 3 |
Mock up desired datagrid
|Property1| A | B |
| 1 | 1.25 | |
| 2 | | 2 |
| 3 | | 3 |
There is no limit on what value Property2 can be.
I have a SQL Server four tables 'mapping' table MappingACVP as:
Author_ID | CoAuthor_ID | Venue_ID | Paper_ID | Year
----------------------------------------------------
677 | 42700 | 64309 | 812229 | 2005
677 | 42700 | 64309 | 812486 | 2005
677 | 42700 | 64309 | 818273 | 2005
677 | 42700 | 65182 | 812229 | 2005
... | ... | ... | ... | ...
... | ... | ... | ... | ...
By using Entity Framework, I got auto-generated code for all four tables included in Entity Framework Model i.e. Authors.cs, CoAuthors_New.cs, Venues_New.cs and Papers_New.cs as well, whereas tables other than Authors all have Author_ID as foreign key as a relationship.
The auto-generated code for class Authors.cs is as:
public partial class Authors
{
public Authors()
{
this.CoAuthors_New = new HashSet<CoAuthors_New>();
this.Papers_New = new HashSet<Papers_New>();
this.Venues_New = new HashSet<Venues_New>();
}
public int id { get; set; }
public int Author_ID { get; set; }
public string Author_Name { get; set; }
public virtual ICollection<CoAuthors_New> CoAuthors_New { get; set; }
public virtual ICollection<Papers_New> Papers_New { get; set; }
public virtual ICollection<Venues_New> Venues_New { get; set; }
}
Now if I want to declare a list as:
List<Authors> _eAthors = new List<Authors>();
and want to fetch values for filling this list from database (using MappingACVP table), whereas there is no Year property in Authors.cs class. So,
How will I fill eAuthors list from database?
I have the bellow collection of objects with master detail data. I want to bind that collection to a datagrid. When user adds new OrderItem it will be reflected in new column which will be dynamically created. So for example one order can have 1 or 10ths order items (columns). I am flattening that Order - OrderItem in new object / CollectionView and binding it to datagrid. However, after the flattening I am not sure how get the Checkboxes states from Datagrid which will be used later for saving.
public class Order
{
public string Code { get; set; }
public string Customer{ get; set; }
public ICollection<OrderItem> Items { get; set; }
}
public class OrderItem
{
public string Name{ get; set; }
public bool Received { get; set; }
}
| Order.Code | Order.Customer| OrderItem.Name| OrderItem.Name| OrderItem.Name|
| 123 | ABC | TRUE | TRUE | TRUE |
| 456 | CDF | TRUE | TRUE | FALSE |
| 789 | EFG | TRUE | FALSE | FALSE |
I`m creating my first app,student grades book, and now i have a problem. I have a txt file full of student info(1 student for each line) and i need to link each student with their marks(they are in other file).What way do you suppose to do it? Maybe I need to make a structure of student name and 2d array?
P.S. Sorry for bad english
Here`s what i mean
Student name lastname
// ---------------------------------------------------------
// |Science |1 |2 |3 |4 |5 |6 |7 |8 |9 |10|11|12|13|14|15|
// ---------------------------------------------------------
// |Maths | | | | | | | | | | | | | | | |
// |English | | | | | | | | | | | | | | | |
1,2,3,4 and etc. is student grade index
A suggestion:
public class Student
{
public Student()
{
Marks = new List<StudentMark>();
}
public string Name { get; set; }
public List<StudentMark> Marks { get; set; }
public void Load(string line)
{
string[] parts = line.Split(' ');
Name = parts[0];
//Other properties, if any:
//LastName = parts[1];
}
}
public class StudentMark
{
public float Mark { get; set; }
public string Lesson { get; set; }
}
I am unsure as to how complex your program is, but would it be an option to create a Student object within which you would save all of the student's information including name and average grade? This would then allow you to save other relavant information. Otherwise, yes it would be an option to look into the dictionary class of the c# langugage. http://msdn.microsoft.com/en-us/library/xfhwa508.aspx
Do you have control of the generation of the separate student and score files? If so can you assign a unique id to each student and store both in each file? This would provide the link between the two. You could add the id as a member of #mahmoodvcs' solution. Then add logic to parse the data by id to get the relevant scores for each student.