Develop Reference

How to reference property of another object if the current object's property is null

I have a public Dictionary<string, PostRenewalActionJobs> Jobs to store some actions I would like to trigger for specific accounts, the key of this dictionary being the account name.
public class PostRenewalActionJobs
{
public List<AlterDatabaseLinkJob> AlterDataBaseLink { get; set; }
public DatabaseConnectionCheckJob DatabaseConnectionCheck { get; set; }
public UnlockDatabaseAccountJob UnlockDatabaseAccount { get; set; }
public LinuxConnectionCheckJob LinuxConnectionCheck { get; set; }
public WindowsConnectionCheckJob WindowsConnectionCheck { get; set; }
public ReplacePasswordInFileJob ReplacePasswordInFile { get; set; }
}
The properties of PostRenewalActionJobs type (AlterDataBaseLink, DatabaseConnectionCheck, etc) can be defined for a specific account or for all accounts by using * as key in the dictionary:
By using below method I am able to retrieve the jobs for an account (if exists) or the general jobs:
public PostRenewalActionJobs GetJobsForAccount(string accountName)
{
return Jobs.ContainsKey(accountName) ? Jobs[accountName] : Jobs["*"];
}
I would like to have a dynamic way of getting a job from the all accounts object ("*") if the one from the specific account is null.
Something like below but whit out repeating the same code for all job types and also a solution that should work when new job types are introduced.
var dbConCheckJob = GetJobsForAccount("someAccount").AlterDataBaseLink;
if(dbConCheckJob == null || !dbConCheckJob.Any())
{
dbConCheckJob = GetJobsForAccount("*").AlterDataBaseLink
}
I was thinking to use some reflection, but I am not sure how to do it.

You don't need to use reflection. You can already determine whether to get the specific jobs for an account or the generic ones, you could then use a Func to get the job you want:
public TJob GetPostJobForAccount<TJob>(string accountName,
Func<PostRenewalActionJobs, TJob> jobSelector) where TJob : JobBase
{
var genericJobs = Jobs["*"];
var accountJobs = Jobs.ContainsKey(accountName) ? Jobs[accountName] : genericJobs;
// Account might be defined but without any job of the given type
// hence selecting from the defaults if need be
return jobSelector(accountJobs) ?? jobSelector(genericJobs);
}
var bobJob = GetPostJobForAccount("bob", x => x.WindowsConnectionCheck);
var aliceJob = GetPostJobForAccount("alice", x => x.UnlockDatabaseAccount);

I found a way to do it, not sure if there is a better way:
public TJob GetPostJobForAccount<TJob>(string accountName)
{
Type type = typeof(PostRenewalActionJobs);
var accountJobs = Jobs[accountName];
var generalJobs = Jobs["*"];
foreach (var item in type.GetProperties())
{
var itemType = item.PropertyType;
var currentType = typeof(TJob);
if (itemType != currentType)
{
continue;
}
var output = (TJob)accountJobs?.GetType()?.GetProperty(item.Name)?.GetValue(accountJobs, null);
if (output is null)
{
output = (TJob)accountJobs?.GetType()?.GetProperty(item.Name)?.GetValue(generalJobs, null);
}
return output;
}
return default;
}

Why does the "contains" method returns an element that is in the list as if it is not?

I have a Product table in my DB. Also, I have Brand and Category tables in my DB which are not related to each other. I want to relate these. In the form UI when I click the one of the Categories, should come the Brands which they have products in the related category.
I tried this way to do this. First, I get my products by categoryID with GetList method then I get these products' brands and I added these brands to pblist list(Brand type). However, some products have the same brands and pblist have repeated brand names. I tried to fix this with contains method but it does not work. Also, I have the same problem in the other part which I try to remove brands not included in pblist from blist(all brands' list). I tried removing item from blist by taking its index with this code: blist.RemoveAt(blist.IndexOf(item)); but this one also not working.It returns -1. But item is in the blist.
public class BrandVM : BaseVM
{
public int ProductCount { get; set; }
}
public class BaseVM
{
public int ID { get; set; }
public string Name { get; set; }
public override string ToString()
{
return this.Name;
}
public class BrandService : ServiceBase, IBrandService
{
public List<BrandVM> GetList(int Count)
{
try
{
var result = GetQuery();
result = Count > 0 ? result.Take(Count) : result;
return result.ToList();
}
catch (Exception ex)
{
return null;
}
}
public List<BrandVM> GetListByCatID(int pCatID)
{
var plist = productService.GetListByCatID(pCatID);
List<BrandVM> pblist = new List<BrandVM>();
foreach (var item in plist)
{
if (!pblist.Contains(item.Brand))
{
pblist.Add(item.Brand);
}
};
var blist = GetList(0);
var blistBackup = GetList(0);
foreach (BrandVM item in blistBackup)
{
if (!pblist.Contains(item))
{
blist.Remove(item);
}
};
return blist;
}
These are my classes related to Brand. In BrandService I shared the filled methods there are more methods to fill.
This is method is in my ProductService:
I use that method to pull product list by CategoryID (plist)
public List<ProductVM> GetListByCatID(int EntityID)
{
try
{
var result = GetQuery().Where(x => x.Category.ID==EntityID);
return result.ToList();
}
catch (Exception ex)
{
return null;
}
}
This GetQuery method for ProductService, in other services there are some differences but there are similar
private IQueryable<ProductVM> GetQuery()
{
return from p in DB.Products
select new ProductVM
{
ID = p.ProductID,
Name = p.ProductName,
UnitPrice = (decimal)p.UnitPrice,
Category =p.CategoryID==null?null:new CategoryVM()
{
ID = (int)p.CategoryID,
Name = p.Category.CategoryName
},
Brand = p.BrandID == null ? null :
new BrandVM
{
ID=(int)p.BrandID,
Name=p.Brand.BrandName,
}
};
}

Entity framework will translate Linq queries into SQL statements, which means that Equals (and GetHashCode) will not be used for comparison of database objects. However, if you're comparing local instances of these objects, then these methods will be used for comparisons.
The default Equals does a reference comparison to determine equality, which literally means that two instances of a type are only considered equal if they both refer to the exact same object in memory.
Instead, we want to use the ID property for equality comparison, which means we need to override the Equals (and GetHashCode) methods for the class.
Here's an example of how you could do this:
public class BaseVM
{
public int ID { get; set; }
public string Name { get; set; }
public override string ToString()
{
return Name;
}
public override bool Equals(object obj)
{
return obj is BaseVM &&
((BaseVM) obj).ID == ID;
}
public override int GetHashCode()
{
return ID;
}
}
Alternatively, if you don't want to modify the class (which I would recommend since it solves this problem everywhere), you can modify your code to filter out any brands that have the same id (or name):
foreach (var item in plist)
{
// Note: you could potentially use 'Name' instead of 'Id'
if (!pblist.Any(productBrand => productBrand.Id == item.Brand.Id))
{
pblist.Add(item.Brand);
}
}

Since you don't ensure that two different instances for a same brand are not equal,
in the sense that ´.Equals(object other)´ returns true,
the ´.Contains´ method as no way to identify them.
I think you'ĺl solve you issue by overriding .Equals in you Brand class.

C# How to find index of a object in listbox datasource (binded with List<T>) by Linq

I have a viewmodel class like this:
public class ViewItem
{
private No as int;
private Name as string;
...Getter-Setter go here...
}
I have a listbox name LbxItemBox
I binded it with datasource is:
List<ViewItem> DataList;
LbxItemBox.Datasource = DataList;
Data final are:
Item1: 1, "Frank"
Item2: 2, "Bob"
Item3: 3, "Johh"
Item4: 4, "Lucis"
How I can find index of a object model like this in LbxItemBox:
ViewItem ViewX = new ViewItem();
ViewX.No = 3;
ViewX.Name = "John";
I tried simple way, not Linq:
int IndexMatched = LbxItemBox.Items.IndexOf(ViewX);
but return -1;
How can I use Linq to find index of what I need?
Thanks for your helps

There are a couple ways you can achieve this. First, you can override Equals for your ViewItem class. This will cause the IndexOf call with a new instance of ViewItem to say that any object you already have in the list is equivalent to a newly created object with the same information. For your class you have listed here is how you could do that:
public class ViewItem
{
private int No { get; set; }
private string Name { get; set; }
public ViewItem(int no, string name)
{
this.No = no;
this.Name = name;
}
public override bool Equals(Object obj)
{
// Check for null values and compare run-time types.
if (obj == null || GetType() != obj.GetType())
return false;
ViewItem other = (ViewItem) obj;
return (No == other.No);
}
}
Your example above should return the right index, given that Equals has been overridden. For more information on correctly implementing Equals and GetHashCode see MSDN or http://www.loganfranken.com/blog/687/overriding-equals-in-c-part-1/.
An alternative way to handle this using linq if you are not looking for true equality would be to match on certain properties of your ViewItem class. Here is an example of doing so:
List<ViewItem> items = new List<ViewItem>() { new ViewItem(1, "John"), new ViewItem(2, "Jake"), new ViewItem(2, "Frank")};
var john = new ViewItem(1, "John");
var frankInd = items.FindIndex(i => i.Name == "Frank");
Console.WriteLine(items.IndexOf(john));
Console.WriteLine(frankInd);

Using LINQ (Enumerable.Cast<TResult> Method):
int IndexMatched = LbxItemBox.Items.Cast<ViewItem>().ToList().FindIndex(x => x.No == ViewX.No);

dynamic queries in dapper

I am trying to work with this. I have written a unit test as a starter for ten like so:
[Fact]
public void TestOredGuids()
{
// Arrange
const string expectedSql = "SELECT * FROM Products WHERE SomeExternalForeignKey = #SomeExternalForeignKey OR Name = SomeExternalForeignKey = #SomeExternalForeignKey";
// Act
var result = DynamicQuery.GetDynamicQuery<Product>("Products", p => p.SomeExternalForeignKey == new Guid("28D3BCFB-9472-4141-BD88-BE5E7E1230F0") || p.SomeExternalForeignKey == new Guid("0F0DBA45-F842-4E46-9ED4-F50B5BCF0509"));
// Assert
}
internal class Product
{
public string Name { get; set; }
public decimal Price { get; set; }
public DateTime ExpiryDate { get; set; }
public int CategoryId { get; set; }
public Guid SomeExternalForeignKey { get; set; }
}
Unfortunately, I am always getting:
Additional information: 'System.Linq.Expressions.NewExpression' does not contain a definition for 'Value'
in the WalkTree method. Am I using GetDynamicQuery wrongly?
If there are any other implementation of dynamic sql mappers like this for dapper, I would appreciate any pointers. Thanks!

From what I see in the source code of the component you are trying to use, it expects the right operand of the expression to be a ConstantExpression (although for some unknown reason the author is using dynamic and expects a Value property), so to make it work, modify you code as follows
var someExternalForeignKey1 = new Guid("28D3BCFB-9472-4141-BD88-BE5E7E1230F0");
var someExternalForeignKey2 = new Guid("0F0DBA45-F842-4E46-9ED4-F50B5BCF0509");
var result = DynamicQuery.GetDynamicQuery<Product>("Products", p => p.SomeExternalForeignKey == someExternalForeignKey1 || p.SomeExternalForeignKey == someExternalForeignKey2);
Update: It turns out that the above also doesn't work, because of course it produces a closure which is not ConstantExpression. To make it work (as well as your original code), here are the required modifications of the DynamicQuery class
private static void WalkTree(BinaryExpression body, ExpressionType linkingType,
ref List<QueryParameter> queryProperties)
{
if (body.NodeType != ExpressionType.AndAlso && body.NodeType != ExpressionType.OrElse)
{
string propertyName = GetPropertyName(body);
var propertyValue = GetPropertyValue(body.Right);
string opr = GetOperator(body.NodeType);
string link = GetOperator(linkingType);
queryProperties.Add(new QueryParameter(link, propertyName, propertyValue, opr));
}
else
{
WalkTree((BinaryExpression)body.Left, body.NodeType, ref queryProperties);
WalkTree((BinaryExpression)body.Right, body.NodeType, ref queryProperties);
}
}
private static object GetPropertyValue(Expression source)
{
var constantExpression = source as ConstantExpression;
if (constantExpression != null)
return constantExpression.Value;
var evalExpr = Expression.Lambda<Func<object>>(Expression.Convert(source, typeof(object)));
var evalFunc = evalExpr.Compile();
var value = evalFunc();
return value;
}
But note that the whole class (as the author states) is just an example, and for instance maps just one parameter (thus one value) per property, so in order to make it really useful, the GetDynamicQuery method needs additional work. You might try this one instead. Hope that helps.

Get properties of class by order using reflection

Please refer to this code
public class A : B
{
[Display(Name = "Initial Score Code", Order =3)]
public Code { get; set; }
[Display(Name = "Initial Score Code", Order =2)]
public Name{ get; set; }
............
}
I need to get all properties of class through order by orderAttribute of Display. I have tried with this code to do
var prop = typeof(A)
.GetProperties()
.OrderBy(p => ((DisplayAttribute)p.GetCustomAttributes(typeof(DisplayAttribute), true).FirstOrDefault).Order);
but it causes an error
object reference not to set an instance of object
I assumed this issue because of some property not having "Order" property in "DisplayAttribute" .
How to handle this kind of situation? I need to order all the properties even though some property not having the value of order property.

You are missing brackets () on FirstOrDefault operator. Also you should deal with case when default value is returned. I suggest to select Order value before getting first or default value. That will return 0 for all properties which don't have DisplayAttribute:
var prop = typeof(A)
.GetProperties()
.OrderBy(p => p.GetCustomAttributes(typeof(DisplayAttribute), true)
.Cast<DisplayAttribute>()
.Select(a => a.Order)
.FirstOrDefault());
If you want properties without DisplayAttribute to be last, you can provide Int32.MaxValue as default value to be returned:
.Select(a => a.Order)
.DefaultIfEmpty(Int32.MaxValue)
.First()

Try this:
var props = from p in typeof(A).GetProperties()
let orderAttribute = (DisplayAttribute)(p.GetCustomAttributes(typeof(DisplayAttribute), true))
.FirstOrDefault()
where orderAttribute != null
orderby orderAttribute.Order
select p;
Or:
var props = from p in typeof(A).GetProperties()
let orderAttribute = (DisplayAttribute)(p.GetCustomAttributes(typeof(DisplayAttribute), true))
.FirstOrDefault()
orderby orderAttribute == null ? 0 : orderAttribute.Order
select p;

Here is a much more complete answer that allows you to better control the ordering of PropertyInfo instances without DisplayAttribute attributes:
public class A
{
[Display(Name = "Initial Score Code", Order = 3)]
public int Code
{
get;
set;
}
[Display(Name = "Initial Score Code", Order = 2)]
public string Name
{
get;
set;
}
}
public class PropertyInfoComparer : IComparer<PropertyInfo>
{
public int Compare(PropertyInfo x, PropertyInfo y)
{
var attribute1 = (DisplayAttribute)x.GetCustomAttributes(typeof(DisplayAttribute)).FirstOrDefault();
var attribute2 = (DisplayAttribute)y.GetCustomAttributes(typeof(DisplayAttribute)).FirstOrDefault();
// If the first property has no attribute, sort it first
if (attribute1 == null)
{
return -1;
}
// If the second property has no attribute, sort it first
if (attribute2 == null)
{
return 1;
}
// Compare the Order properties of both attributes
return attribute1.Order.CompareTo(attribute2.Order);
}
}
[AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
public class DisplayAttribute : Attribute
{
public string Name
{
get;
set;
}
public int Order
{
get;
set;
}
}
Usage:
// Get all the properties of Foo and order them using PropertyInfoComparer
typeof(Foo).GetProperties().OrderBy(arg => arg, new PropertyInfoComparer());

I like the approach with Comparer. However, when I tried it, my iterator went into a dead loop at first. Later, it started throwing exceptions. Also, I optimized it for the case when first property doesn't contain "Order" descriptor to avoid even checking for a second one. I also moved all comments into the class description:
/// <summary>
/// If the first property has no attribute, sort it first
/// If the second property has no attribute, sort it first
/// Compare the Order properties of both attributes
/// </summary>
public class PropertyInfoComparer : IComparer<PropertyInfo>
{
public int Compare(PropertyInfo x, PropertyInfo y)
{
if (x == y) return 0;
var attrX = (DisplayAttribute)x.GetCustomAttributes(typeof(DisplayAttribute)).FirstOrDefault();
int? orderX = attrX?.GetOrder();
if (orderX == null) return -1;
var attrY = (DisplayAttribute)y.GetCustomAttributes(typeof(DisplayAttribute)).FirstOrDefault();
int? orderY = attrY?.GetOrder();
if (orderY == null) return 1;
return ((int)orderX).CompareTo((int)orderY);
}
}
Unfortunately, classes that have properties without the "Order" descriptor lose their "natural" order. Therefore, I ended up checking for any properties that have the "Order" descriptor first. If at least one of them has that descriptor, then do the sorting.