I have this sentence linq, with select inside a select using a two viewmodels, the problem is that
in my loginviewmodel not all have a status equal to received, there may be nulls, but when putting them in my view some columns in my grid appear empty, I would like to see N/A appear by default if logviewmodel is = null but I don't know how to do it, I return this as JSON since I'm using datatable on the server side, I don't know if manipulating the json can also be done
I Share my linq sentence
var result = db.document.Select(d => new DocumentViewModel
{
DocumentId = d.DocumentId,
Name = w.name
ReceivedLogs = d.Logs
.Where(l => l.Status == Status.Received)
.Select(l => new LogViewModel
{
CurrentApprover = l.User,
NameApprover = l.User.FullName
}).FirstOrDefault()
}).ToList();
thanks
You can check if FirstOrDefault() returns null and then use a default LogViewModel:
var result = db.document.Select(d => new DocumentViewModel
{
DocumentId = d.DocumentId,
Name = w.name
ReceivedLogs = d.Logs
.Where(l => l.Status == Status.Received)
.Select(l => new LogViewModel
{
CurrentApprover = l.User,
NameApprover = l.User.FullName
}).FirstOrDefault() ?? new LogViewModel {
CurrentApprover = "N/A",
NameApprover = "N/A"
}
}).ToList();
I am trying to fill select tag options from JQuery ajax call. I am using Asp.Net Core 2.1 Razor Pages, and PostgreSQL as DB.
Here is my Server side LINQ code
[HttpGet]
public ActionResult TypeofAccounts()
{
var result = (from N in _POSContext.TypeOfAccounts
select new { label = N.AccountType, id = N.AccountType });
return Json(result);
}
It works fine. Now, I want to sort those results from LINQ so I tried following ways but it always encounters Npgsql Exception "column \"label\" does not exist"
var result = (from N in _POSContext.TypeOfAccounts.OrderBy(x=>x.AccountType)
select new { label = N.AccountType, id = N.AccountType });
var result = (from N in _POSContext.TypeOfAccounts
select new { label = N.AccountType, id = N.AccountType }).OrderBy(x => x.label);
var result = (from N in _POSContext.TypeOfAccounts.OrderBy(x => x.AccountType)
where N.AccountType != null
select new { label = N.AccountType, id = N.AccountType });
I could see coloumn is missing in generated sql.
{SELECT x."AccountType" AS id
FROM "TypeOfAccounts" AS x
WHERE x."AccountType" IS NOT NULL
ORDER BY label}
You need to invoke the query from the database using ToList method, then selecting your object, like this:
var result = _POSContext.TypeOfAccounts
.Where(x => x.AccountType != null)
.OrderBy(x => x.AccountType)
.ToList()
.Select(x =>
new
{
label = x.AccountType,
id = x.AccountType
}
);
You can try this
var result = _POSContext.TypeOfAccounts
.Where(x => x.AccountType != null)
.OrderBy(x => x.AccountType)
.ToList()
.Select(x =>
new
{
label = x.AccountType,
id = x.AccountType
}
);
I want to use the distinct clause for multiple levels. Firstly i tried with DataTable but did't got success so i converted DataTable to AsEnumerable.
My problem here is that the Fields which i have specified/hard coded will be coming dynamic, same for both Where & Select.
How to add dynamic Fields in Where & Select?
DataTable data3 = new DataTable();
var listData = data3.AsEnumerable()
.Where(m => !String.IsNullOrEmpty(m.Field<string>("clientname"))
&& !String.IsNullOrEmpty(m.Field<string>("project"))
&& !String.IsNullOrEmpty(m.Field<string>("postedstate"))
&& !String.IsNullOrEmpty(m.Field<string>("postedcity"))
&& !String.IsNullOrEmpty(m.Field<string>("siteadd")))
.Select(row => new
{
clientname = row.Field<string>("clientname"),
project = row.Field<string>("project"),
postedstate = row.Field<string>("postedstate"),
postedcity = row.Field<string>("postedcity"),
siteadd = row.Field<string>("siteadd")
}).Distinct();
You could do something similar to this:
string clientName = "my client";
string project = null;
DataTable data3 = new DataTable();
var listData = data3.AsEnumerable().Where(m =>
(String.IsNullOrEmpty(clientName) || m.Field<string>("clientname") == clientName)
&& (String.IsNullOrEmpty(project) || m.Field<string>("project") == project)
).Select(row => new Project()
{
clientname = row.Field<string>("clientname"),
project = row.Field<string>("project"),
postedstate = row.Field<string>("postedstate"),
postedcity = row.Field<string>("postedcity"),
siteadd = row.Field<string>("siteadd")
}).Distinct();
This way you will have no need to have an anonymous type returned and get rid of the problem.
I have a query that is currently far too slow.
I am trying to search a Code (a string) on the main page that will bring the user the relevant info.
Eg. The user can search a code from the main page and this will search for the code in Job, Work Phase, Wbs, Work Element, EA, Jobcard and Estimate and return the relevant info.
I make a number of trips to the database to collect the data i need when I believe it can be done in just one.
I have a number of tables that are all linked:
Contracts, Jobs, WorkPhases, Wbss, Engineering Activities, Jobcards and Estimates.
Contracts have a list of Jobs,
Jobs have a list of Workphases,
Workphases have a list of Wbss etc
Is there a quicker way to do this?
public Result Handle(Query query)
{
query.Code = query.Code ?? string.Empty;
var result = new Result();
//result.SetParametersFromPagedQuery(query);
result.Items = new List<Item>();
if (query.SearchPerformed)
{
var contracts = _db.Contracts.AsEnumerable().Where(x => x.Code == query.Code);
result.Items = result.Items.Concat(contracts.Select(x => new Item()
{
Code = x.Code,
Id = x.Id,
Name = x.Name,
Type = MainPageSearchEnum.Contract,
ContractName = x.Name,
Url = string.Format("Admin/Contract/Edit/{0}", x.Id)
})).ToList();
var jobs = _db.Jobs.AsEnumerable().Where(x => x.Code == query.Code);
result.Items = result.Items.Concat(jobs.Select(x => new Item()
{
Code = x.Code,
Id = x.Id,
Name = x.Name,
ContractName = x.Contract.Name,
Type = MainPageSearchEnum.Job,
Url = string.Format("Admin/Job/Edit/{0}", x.Id)
})).ToList();
//var workPhases = _db.WorkPhases.AsEnumerable().Where(x => x.ContractPhase.Code.ToLower() == query.Code.ToLower());
var workPhases = _db.WorkPhases.AsEnumerable().Where(x => x.ContractPhase.Code == query.Code);
result.Items = result.Items.Concat(workPhases.Select(x => new Item()
{
Code = x.ContractPhase.Code,
Id = x.Id,
Name = x.ContractPhase.Name,
Type = MainPageSearchEnum.WorkPhase,
Url = string.Format("Admin/WorkPhase/Edit/{0}", x.Id)
})).ToList();
var wbss = _db.WBSs.AsEnumerable().Where(x => x.Code == query.Code);
result.Items = result.Items.Concat(wbss.Select(x => new Item()
{
Code = x.Code,
Id = x.Id,
Name = x.Name,
Type = MainPageSearchEnum.WBS,
Url = string.Format("Admin/WBS/Edit/{0}", x.Id)
})).ToList();
var eas = _db.EngineeringActivities.AsEnumerable().Where(x => x.Code == query.Code);
result.Items = result.Items.Concat(eas.Select(x => new Item()
{
Code = x.Code,
Id = x.Id,
Name = x.Name,
Type = MainPageSearchEnum.EA,
Url = string.Format("Admin/EngineeringActivity/Edit/{0}", x.Id)
})).ToList();
var jcs = _db.Jobcards.AsEnumerable().Where(x => x.Code == query.Code);
result.Items = result.Items.Concat(jcs.Select(x => new Item()
{
Code = x.Code,
Id = x.Id,
Name = x.Name,
Type = MainPageSearchEnum.EA,
Url = string.Format("Admin/JobCard/Edit/{0}", x.Id)
})).ToList();
var estimates = _db.Estimates.AsEnumerable().Where(x => x.Code == query.Code);
result.Items = result.Items.Concat(estimates.Select(x => new Item()
{
Code = x.Code,
Id = x.Id,
Name = x.Name,
Type = MainPageSearchEnum.Estimate,
Url = string.Format("Estimation/Estimate/Edit/{0}", x.Id)
})).ToList();
}
return result;
}
Disclaimer: I'm the owner of the project Entity Framework Plus
This library has a Query Future feature which allows batching multiple queries in a single roundtrip.
Example:
// using Z.EntityFramework.Plus; // Don't forget to include this.
var ctx = new EntitiesContext();
// CREATE a pending list of future queries
var futureCountries = ctx.Countries.Where(x => x.IsActive).Future();
var futureStates = ctx.States.Where(x => x.IsActive).Future();
// TRIGGER all pending queries in one database round trip
// SELECT * FROM Country WHERE IsActive = true;
// SELECT * FROM State WHERE IsActive = true
var countries = futureCountries.ToList();
// futureStates is already resolved and contains the result
var states = futureStates.ToList();
Wiki: EF+ Query Future
Have you tried the Union / UnionAll operator?
It's purpose is exactly like you wish - combine the identical data from different sources.
Furthermore due to the concept of deferred execution your query will only be executed when you actually iterate over the result (or call a method that does that, for example - .ToList()
var contractsQuery = _db.Contracts.AsEnumerable().Where(x => x.Code == query.Code).Select(x=>new {Code=x.Code, Id=x.Id, ...});
var jobsQuery = _db.Jobs.AsEnumerable().Where(x => x.Code == query.Code).Select(x=>new{Code=x.Code, Id=x.Id, ...});
var workPhasesQuery = _db.WorkPhases.AsEnumerable().Where(x => x.ContractPhase.Code == query.Code).Select(x=>new{Code=x.Code, Id=x.Id, ...});
// and so on
var combinedQuery = contractsQuery.UnionAll(jobsQuery).UnionAll(workPhasesQuery ).UnionAll(...
var result = combinedQuery.ToList();
A similar question is Union in linq entity framework
Another code sample can be found here
Please notice that this is exactly the same concept of manipulating data as in T-SQL union, and under the covers you will get an sql query using a union operator
Yes there most certainly is a way to query multiple tables. You can use the Include() method extension for your query. for instance:
var examplelist = _db.Contracts.(v => v.id == "someid" && v.name == "anotherfilter").Include("theOtherTablesName").ToList();
You can include as many tables as you like this way. This is the recommended method.
You can also use the UnionAll() method but you'd have to define your queries separately for this
I want to get my last record in the table
I use this code but it returns nothing
var a = new DataClasses1DataContext();
var student = db.tbl_farmers.OrderByDescending(s => s.id).FirstOrDefault();
dataGridView1.DataSource = student;
In LINQ we achieve the same thing with the help of OrderByDescending function and Take function.
var qry = db.ObjectCollection
.Where(m => m.<field> == data)
.OrderByDescending(m => m.<field>)
.Take(n);
Try this
var a = new DataClasses1DataContext();
var student = db.tbl_farmers.OrderByDescending(s => s.id).Take(1);
dataGridView1.DataSource = student;ode here