I have this piece of code, that checks whether a returned object is null. If so, it will return 0, or else it will return a property inside the object.
var userPoints = (from Point p in entities.Point
where p.UserName == userName
select p).SingleOrDefault();
if (userPoints == null)
{
return 0;
}
else
{
return userPoints.Points;
}
Is it possible to simplify the if statements with the nullable operator? I've tried this, but the system throws an exception when attempting to read the property
return userPoints.Points ?? 0;
No, unfortunately there's nothing which will do exactly that. Options:
Use the conditional operator:
return userPoints == null ? 0 : userPoints.Points;
Change your query to make that do the defaulting:
return (from Point p in entities.Point
where p.UserName == userName
select p.Points).SingleOrDefault();
Personally I'd go for the latter approach :) If you wanted a default other than 0, you'd need something like:
return (from Point p in entities.Point
where p.UserName == userName
select (int?) p.Points).SingleOrDefault() ?? -1;
You can do this:
var userPoints = (from Point p in entities.Point
where p.UserName == userName
select p.Point).SingleOrDefault();
return userPoints;
If there are no results then userPoints will be 0, otherwise it will be the value of Points.
You can't use it in your context.
Explanation:
You want to check whether userPoints is null, but want to return userPoints.Points if it is not null.
The ?? operator checks the first operand for null and returns it, if it is not null. It doesn't work if what you want to check and what you want to return are two different things.
Hover over var with the mouse and see what type it is.
Related
I have an object media that holds descriptions which is a list. I'd love to see some elegant logic in Kotlin to add an element to that descriptions if the field is not null or add a fresh new list (with an initial element) to that field if it is null.
Pseudo:
if (media.descriptions == null) { media.descriptions = listOf("myValue")}
else { media.descriptions.add("myValue") }
I would probably do it the other way around, except you need to alter media itself (see below), i.e. creating your list first and add all the other entries to that list if media.descriptions isn't null:
val myDescriptions = mutableListOf("myValue") // and maybe others
media.descriptions?.forEach(myDescriptions::add)
If you need to manipulate descriptions of media, there is not so much you can do to make it more readable...:
if (media.descriptions == null) {
media.descriptions = mutableListOf("myValue") // just using mutable to make it clear
} else {
media.descriptions += "myValue"
}
or maybe:
if (media.descriptions == null) {
media.descriptions = mutableListOf<String>()
}
media.descriptions?.add("myValue")
You can use the elvis ?: operator to assign the list.
The simplest way I can think of is
media.descriptions = media.descriptions ?: listOf("myValue")
media.descriptions.add("myValue")
what is wrong with this linq query that show me the error of Does not contain a definition for 'union'
(from rev in db.vM29s
where Years.Contains(rev.FinancialYear) && rev.Exclude=="No"
group rev by new { rev.RevenueCode, rev.FinancialYear } into g
select new
{
Revenuecode = g.Key.RevenueCode,
totalRevenue = g.Sum(x => x.RevenueAmount),
RevenueEnglish = (from a in db.RevenueCodes where a._RevenueCode == g.Key.RevenueCode select a.RevenueEng).FirstOrDefault(),
// MinorCode = (from a in db.MinorCodes where a._MinorCode == g.Key.MinorCode select a.MinorEng),
RevenueDari = (from a in db.RevenueCodes where a._RevenueCode == g.Key.RevenueCode select a.RevenueDari).FirstOrDefault(),
Yearss = g.Key.FinancialYear
}
)
.Union
(from u in db.rtastable
where Years.Contains(u.Year)
group u by new { u.objectcode, u.Year } into g
select new
{
Revenuecode = g.Key.objectcode,
totalRevenue = g.Sum(x => x.amount),
RevenueEnglish = (from a in db.RevenueCodes where a._RevenueCode == g.Key.objectcode select a.RevenueEng).FirstOrDefault(),
// MinorCode = (from a in db.MinorCodes where a._MinorCode == g.Key.MinorCode select a.MinorEng),
RevenueDari = (from a in db.RevenueCodes where a._RevenueCode == g.Key.objectcode select a.RevenueDari).FirstOrDefault(),
Yearss = g.Key.Year
}
)
.ToList();
If you included using System.Linq; and both Anonymous Types have exactly the same property names + property types, then what you did should work.
Yet it does not work. The solution is to check your Anonymous Types for subtle property name differences and/or subtle property type differences.
E.g. even an int vs a smallint or double or decimal will cause this build error:
'System.Collections.Generic.IEnumerable<AnonymousType#1>' does not contain a definition for 'Union' and the best extension method overload 'System.Linq.Queryable.Union(System.Linq.IQueryable, System.Collections.Generic.IEnumerable)' has some invalid arguments
Switching to .Concat() will not fix this: it has the same (obvious) restriction that the types on both sides must be compatible.
After you fix the naming or typing problem, I would recommend that you consider switching to .Concat(). The reason: .Union() will call .Equals() on all objects to eliminate duplicates, but that is pointless because no two Anonymous Objects that were created independently will ever be the same object (even if their contents would be the same).
If it was your specific intention to eliminate duplicates, then you need to create a class that holds your data and that implements .Equals() in a way that makes sense.
You should use Concat or using addRange if the data is allready in memory.
How do you preset fields so that (unless a specific value is entered from the form itself) they STAY null? For another project, I will later have to pull information from this table depending on what options people choose, so if I could do a cfif against nulls I think it'd be a lot easier than the blanks that are currently generated if I don't insert any new values.
Does anyone know where/how to do this? I'm using Microsoft's SQL Server Management Studio to edit what the individual columns, and all I can find are the command codes using INSERT, SELECT, etc., rather than having a list that I edit. Or is that the only way to make my default setting be "null"?
Thanks for the help
If a field is set to be a nullable field (that is, it allows NULL), when adding a row, it will be NULL unless otherwise specified.
You don't need to do anything special for this.
If your INSERT and UPDATE statements simply omit the field, it will not be updated, though you can specifically specify NULL for such a field if wanted.
You could use a helper function to handle parameter setup. This is a simplified version of a function I use...
private static object ProcessParameter(object input)
{
if (input == null)
return input;
switch (input.GetType().ToString().ToLower())
{
case "system.string":
if (input == null || input.ToString() == "") { return DBNull.Value; }
return input;
case "system.int32":
case "system.double":
if (input.ToString() == "0" && IsNullable(input)) { return DBNull.Value; }
return input;
case "system.datetime":
if (System.Convert.ToDateTime(input) == DateTime.MinValue || System.Convert.ToDateTime(input) == default(DateTime)) { return DBNull.Value; }
return input;
default:
return input;
}
}
How come my if statement if (tablename == Character.toString('S')) is not registering as true? Both print out the be S... Is there a different why I can implement this? I could do a != but I need to add more arguments to my if statement, and my tablename needs to stay a string.
System.out.println("Enter table:");
String line = input.readLine();
StringTokenizer tk = new StringTokenizer(line);
String tablename = tk.nextToken();
DatabaseMetaData d = conn.getMetaData();
ResultSet rm = d.getColumns(null, null, tablename, null);
System.out.println(tablename);
System.out.println(Character.toString('S');
System.out.println(tablename == Character.toString('S');
if (tablename == Character.toString('S')){
System.out.println("Woot!");
}
OUTPUT:
Enter table:
S
S
S
false
Since you're comparing both objects for equality, you need to use:
if (tablename.equals(Character.toString('S'))) {
...
Here's a nice reference on equality comparison in java:
http://leepoint.net/notes-java/data/expressions/22compareobjects.html
The == only relates to the equality of the pointer that Character.toString() returns. Need to use the below.
tablename.equals(Character.toString('s'))
I'm trying to retrieve a list of orders based on parameters specified by a user (basic search functionality). The user will enter either an orderId or a bunch of other params, those will get wrapped up into a message, and eventually make their way to the method below. My question is, how do I only look at the parameters that actually have values? So if a user were to enter a received date range and a store number and all other fields were null, I want to return orders for stores received in the date range and ignore all the null parameters. At first I was thinking I could use a conjunction, but I can't see a way to ignore the null parameters. Then I started splitting things out into the if statements below the main expression, but I don't want to look at those criteria if the user provides an externalId. Is there a simple way to do this?
public IList<Core.Order> GetOrderByCriteria
(
string ExternalId,
int? Store,
int? Status,
DateTime? beforeTransmissionDate, DateTime? afterTransmissionDate,
DateTime? beforeAllocationProcessDate, DateTime? afterAllocationProcessDate,
DateTime? beforeReceivedDate, DateTime? afterReceivedDate
)
{
try
{
NHibernate.ICriteria criteria = NHibernateSession.CreateCriteria(typeof(Core.Order))
.Add(Expression.Or
(
Expression.Like("ExternalId", ExternalId),
Expression.Conjunction()
.Add(Expression.Between("ReceivedDate", beforeReceivedDate, afterReceivedDate))
.Add(Expression.Between("TransmissionDate", beforeTransmissionDate, afterTransmissionDate))
.Add(Expression.Between("AllocationProcessDate", beforeAllocationProcessDate, afterAllocationProcessDate))
)
);
if(Store.HasValue)
criteria.Add(Expression.Eq("Status", Status));
if(Status.HasValue)
criteria.Add(Expression.Eq("Store", Store));
return criteria.List<Core.Order>();
}
catch (NHibernate.HibernateException he)
{
DataAccessException dae = new DataAccessException("NHibernate Exception", he);
throw dae;
}
}
I wound up dropping the whole conjunction thing and replacing the code in the try block with the code below. I also used joins which reduced the number of db accesses and reduced the amount of code needed.
NHibernate.ICriteria criteria = NHibernateSession.CreateCriteria(typeof(Core.Order));
if (!String.IsNullOrEmpty(ExternalId))
{
criteria.Add(Expression.Like("ExternalId", ExternalId));
}
if (beforeReceivedDate != null && afterReceivedDate != null)
criteria.Add(Expression.Between("ReceivedDate", beforeReceivedDate, afterReceivedDate));
if (beforeTransmissionDate != null && afterTransmissionDate != null)
criteria.Add(Expression.Between("TransmissionDate", beforeTransmissionDate, afterTransmissionDate));
if (beforeAllocationProcessDate != null && afterAllocationProcessDate != null)
criteria.Add(Expression.Between("AllocationProcessDate", beforeAllocationProcessDate, afterAllocationProcessDate));
if (Store.HasValue)
criteria.CreateCriteria("Store", "Store").Add(Expression.Eq("Store.LocationNumber", Store.Value));
return criteria.List<Core.Order>();
I had to do something similar not long ago. I'm pretty sure you can modify this to fit your needs.
private ICriteria AddSearchCriteria(ICriteria criteria, string fieldName, string value)
{
if (string.IsNullOrEmpty(fieldName))
return criteria;
if(string.IsNullOrEmpty(value))
return criteria;
criteria.Add(Expression.Like(fieldName, "%" + value + "%"));
return criteria;
}
The code calling the method ended up looking like this:
var query = session.CreateCriteria(typeof (User));
AddSearchCriteria(query, "FirstName", form["FirstName"]);
AddSearchCriteria(query, "LastName", form["LastName"]);
var resultList = new List<User>();
query.List(resultList);
return resultList;
Leave it up to the function to determine if the input is valid and whether to return the unmodified ICriteria or to add another Expression before returning it.