I have the below codes :
var predicate = PredicateBuilder.True().And(p => p["_latestversion"] == "1");
predicate = predicate.And(GetDefaultTemplatePredicatesExpression());
if(!string.IsNullOrEmpty(path))
predicate = predicate.And(GetPathPredicateExpression(path));
var results = context.GetQueryable().Where(predicate).OrderByDescending(p=> p.Views).GetResults();
if (results != null)
{
if (results.Hits.Any())
{
return results.Hits.Select(x => x.Document).ToList();
}
}
I am retrieving a list of records based on the latest version. But this code does not indicate the number of records to return back. Can I check whether does the above codes return whatever number of records that it retrieve from the database?
It's unclear to me what that GetResults() call would be returning (is that an extension method you've defined? I can't find anything relevant as part of the .NET framework.), which makes it hard to make a firm statement about anything else.
I believe you can split the line:
var results = context.GetQueryable<ArticleItem>()
.Where(predicate)
.OrderByDescending(p=> p.Views)
.GetResults();
into three lines:
var query = context.GetQueryable<ArticleItem>()
.Where(predicate)
.OrderByDescending(p=> p.Views);
var count = query.Count();
var results = query.GetResults();
Which I think will give you would you want.
Related
I am working on a web service. I am using linq to query a database. Seemingly simple, but I've run into an issue. Here is my code for reference:
List<Comment> res = new List<Comment>();
using (ApplicationHistoryEntities ahe = new ApplicationHistoryEntities())
{
res = (from columns in ahe.Comments
where columns.NetforumId == actionuniqueid
select columns).ToList();
}
If I have no entries in the database, will my .ToList() throw an error? I could deploy it, and just try it out but I want to know more about the mechanism that my linq is using. If ahe.Comments database has no rows... what will the (from...) section return?
I could just add a null reference check, use dynamics etc but I want to really understand it.
I found this Q: how to know if my linq query returns null but it seems like all of the answers are in conflict on how it really should be done...
example answers:
Either you can convert it to list and then check the count
Best approach is to check there is null(no items) in list use Any() instead of count()
LINQ queries should never return null and you should not get an exception if the result is empty. You probably have an error in your code.
You can realise the result as a list then check the items.
You can see why I question how it works.
Edit:
Final code looks like this:
List<Comment> res;
using (ApplicationHistoryEntities ahe = new ApplicationHistoryEntities())
{
res = ahe.Comments?.Where(rowItem => rowItem.NetforumId == actionuniqueid).ToList() ??
new List<Comment>().ToList();
}
Look at this example:
List<string> test = new List<string>();
var test1 = test.Where(x => x == "a").ToList();
If test exists but is empty the query returns an empty list. If test is null the query throws an error. So you can adapt the query as follows
List<string> test = new List<string>();
test = null;
var test1 = test?.Where(x => x == "a") ?? new List<string>().ToList();
The query is now 'safe'. Both of the above examples return an empty list i.e. test1.Count() will return zero but will be usable.
You can also look at the definitions of Where and ToList
I am slow today
There is a request
"Take random child and put it into another garden."
I changed the code, but error in the last line of code "Does not contain a definition…and no extension method":
var query = db.Child.Where(x => x.Garden != null);
int count = query.Count();
int index = new Random().Next(count);
var ch = db.Child.OrderBy(x => query.Skip(index).FirstOrDefault());
ch.Garden_Id = "1";
What am I doing wrong?
It's hard to tell what you're doing wrong, because you didn't say why the results you're getting does not satisfy you.
But I can see two possible mistakes.
You're counting items with x.Garden != null condition, but taking from all children.
Take returns IEnumerable<T> even when you specify it to return only 1 item, you should probably use First instead.
I think your k should be
var k = db.Child.Where(x => x.Garden != null).Skip(rnd.Next(0,q)).First();
Does anyone know how to make a Linq query that gets all the birthdays of today? The code below doesn't work :
var getBirthdays =
orgContext.CreateQuery<Contact>()
.Where(c => c.BirthDate != null
&& c.BirthDate.Value.Month == DateTime.Now.Month).ToList();
I get an error like this:
"Invalid 'where' condition. An entity member is invoking an invalid
property or method."
Thanks in advance!
Anytime a vendor writes a four part blog series on how to do something as simple as finding a birthday (as Microsoft did in 2007), you have to know this won't be simple. So far as I can tell, this hasn't updated since then.
Find contacts with upcoming birthdays
Find contacts with upcoming birthdays - Part 2
Find contacts with upcoming birthdays - Parts 3 and 4
So you have limited options:
Make new fields called something like new_birthmonth and new_birthday that's updated every time a contact is created or updated via a plugin, and then query on those int fields.
Using Dynamic Linq, construct an OR clause in your WHERE clause that checks to see if the birthday falls in a reasonable range of years (say, 140 for the long-livers) (code below).
List<string> birthdays = new List<string>(); //will contain list of OR clauses
//makes sure no CRM unsupported dates are passed (less than 1/1/1900)
for (int i = Math.Min(140, DateTime.Today.Year - 1900); i > -1; i--)
{
//adds a different date per year
birthdays.Add
(
string.Format
(
//DateTimes are stored in UTC
"BirthDate = DateTime.Parse(\"{0}\")",
DateTime.Today.ToUniversalTime().AddYears(-i)
)
);
}
//completes the correct dynamic linq OR clause
string birthdayList = string.Join(" OR ", birthdays);
var getBirthdays = orgContext.CreateQuery<Xrm.Contact>()
.Where(c => c.BirthDate != null)
.Where(birthdayList)
.ToList();
I solved my problem based on the example of "Peter Majeed" and using "LinqKit"!
var predicate = PredicateBuilder.False<Contact>();
for (int i = Math.Min(140, DateTime.Today.Year - 1900); i > -1; i--)
{
DateTime cleanDateTime = new DateTime(DateTime.Today.AddYears(-i).Year, DateTime.Today.AddYears(-1).Month, DateTime.Today.AddYears(-i).Day);
predicate = predicate.Or(p => p.BirthDate == cleanDateTime.ToUniversalTime());
}
var getBirthdays = (from c in orgContext.CreateQuery<Contact>().AsExpandable().Where(predicate)
select c).ToList();
The above query gave me the correct result! Thx to all who helped me!
If c.BirthDate is nullable, you have to convert it to a datetime first:
var getBirthdays = orgContext.CreateQuery<Contact>()
.Where(c => c.BirthDate != null &&
(Convert.ToDateTime(c.BirthDate).Month ==
DateTime.Now.Month) &&
Convert.ToDateTime(c.BirthDate).Day ==
DateTime.Now.Day))
.ToList();
You could fetch this info with a Query, if that is possible in your situation?
//set up the condition + filter
var ce = new Microsoft.Xrm.Sdk.Query.ConditionExpression();
ce.Operator = Microsoft.Xrm.Sdk.Query.ConditionOperator.LastXDays;
ce.AttributeName = "birthdate";
ce.Values.Add(30);
var fe = new Microsoft.Xrm.Sdk.Query.FilterExpression();
fe.AddCondition(ce);
//build query
var query = new Microsoft.Xrm.Sdk.Query.QueryExpression();
query.EntityName = "contact";
query.Criteria.AddFilter(fe);
//get results
var results = CrmHelperV5.OrgProxy.RetrieveMultiple(query);
//if you want early bound entities, convert here.
var contacts = new List<Contact>();
foreach(var result in results.Entities)
{
contacts.Add(result.ToEntity<Contact>());
}
You may want to investigate the other operators for the filters + conditions
You can use QueryExpression (it works for Microsoft CRM Plugin)
public EntityCollection getBirthdateList(IOrganizationService orgsService)
{
List<string> birthdays = new List<string>();
//makes sure no CRM unsupported dates are passed (less than 1/1/1900)
for (int i = Math.Min(140, DateTime.Today.Year - 1930); i > -1; i--)
{
//adds a different date per year
birthdays.Add
(
DateTime.Now.AddYears(-i).ToString("yyyy-MM-dd")
);
}
// Instantiate QueryExpression
var query = new QueryExpression("contact");
// Define filter QEquote.Criteria
var queryfilter = new FilterExpression();
query.Criteria.AddFilter(queryfilter);
// Define filter
queryfilter.FilterOperator = LogicalOperator.Or;
queryfilter.AddCondition("birthdate",ConditionOperator.In,birthdays.ToArray());
return orgsService.RetrieveMultiple(query); ;
}
Is there a better way to check if a LINQ projection query returns results:
IList<T> TList = db.Ts.Where(x => x.TId == 1).ToList(); // More canonical way for this?
if (TitleList.Count > 0)
{
// Result returned non-zero list!
string s = TList.Name;
}
You can use Any(), or perhaps more appropriately to your example, SingleOrDefault(). Note that if you are expecting more than one result and plan to use all of them, then it doesn't really save anything to use Any() instead of converting to a List and checking the length. If you don't plan to use all the results or you're building a larger query that might change how the query is performed then it can be a reasonable alternative.
var item = db.Ts.SingleOrDefault( x => x.TId == 1 );
if (item != null)
{
string s = item.Name;
...
}
or
var query = db.Ts.Where( x => x.Prop == "foo" );
if (query.Any())
{
var moreComplexQuery = query.Join( db.Xs, t => t.TId, x => x.TId );
...
}
I have a linq query like this:
var accounts =
from account in context.Accounts
from guranteer in account.Gurantors
where guranteer.GuarantorRegistryId == guranteerRegistryId
select new AccountsReport
{
recordIndex = ?
CreditRegistryId = account.CreditRegistryId,
AccountNumber = account.AccountNo,
}
I want to populate recordIndex with the value of current row number in collection returned by the LINQ. How can I get row number ?
Row number is not supported in linq-to-entities. You must first retrieve records from database without row number and then add row number by linq-to-objects. Something like:
var accounts =
(from account in context.Accounts
from guranteer in account.Gurantors
where guranteer.GuarantorRegistryId == guranteerRegistryId
select new
{
CreditRegistryId = account.CreditRegistryId,
AccountNumber = account.AccountNo,
})
.AsEnumerable() // Moving to linq-to-objects
.Select((r, i) => new AccountReport
{
RecordIndex = i,
CreditRegistryId = r.CreditRegistryId,
AccountNumber = r.AccountNo,
});
LINQ to objects has this builtin for any enumerator:
http://weblogs.asp.net/fmarguerie/archive/2008/11/10/using-the-select-linq-query-operator-with-indexes.aspx
Edit: Although IQueryable supports it too (here and here) it has been mentioned that this does unfortunately not work for LINQ to SQL/Entities.
new []{"aap", "noot", "mies"}
.Select( (element, index) => new { element, index });
Will result in:
{ { element = aap, index = 0 },
{ element = noot, index = 1 },
{ element = mies, index = 2 } }
There are other LINQ Extension methods (like .Where) with the extra index parameter overload
Try using let like this:
int[] ints = new[] { 1, 2, 3, 4, 5 };
int counter = 0;
var result = from i in ints
where i % 2 == 0
let number = ++counter
select new { I = i, Number = number };
foreach (var r in result)
{
Console.WriteLine(r.Number + ": " + r.I);
}
I cannot test it with actual LINQ to SQL or Entity Framework right now. Note that the above code will retain the value of the counter between multiple executions of the query.
If this is not supported with your specific provider you can always foreach (thus forcing the execution of the query) and assign the number manually in code.
Because the query inside the question filters by a single id, I think the answers given wont help out. Ofcourse you can do it all in memory client side, but depending how large the dataset is, and whether network is involved, this could be an issue.
If you need a SQL ROW_NUMBER [..] OVER [..] equivalent, the only way I know is to create a view in your SQL server and query against that.
This Tested and Works:
Amend your code as follows:
int counter = 0;
var accounts =
from account in context.Accounts
from guranteer in account.Gurantors
where guranteer.GuarantorRegistryId == guranteerRegistryId
select new AccountsReport
{
recordIndex = counter++
CreditRegistryId = account.CreditRegistryId,
AccountNumber = account.AccountNo,
}
Hope this helps.. Though its late:)