i have a datatable which i have to assign a primary key if it doesn't already have one. i tried :
if (ds.Tables[0].PrimaryKey == null)
{
ds.Tables[0].PrimaryKey = new DataColumn[] { dt.Columns["Naam"] };
}
But the PrimaryKey (in this case) not null. When i checked it contained : {System.Data.DataColumn[0]} How can i check on that?
Javier's answer is correct, but lacks explanation. So here it is, DataTable.PrimaryKey property is collection of DataColumns.
If the DataTable PrimaryKey property is not set than length of the collection will be 0. If DataTable has one or more fields defined as primary key than length of the PrimaryKey property will reflect this.
So, checking like this:
if (ds.Tables[0].PrimaryKey.Length == 0)
will tell us if no columns are added to represent the primary key, and the part
ds.Tables[0].PrimaryKey = new DataColumn[] { dt.Columns["Naam"] };
would actually add DataColumn(s) to collection of columns held by PrimaryKey property.
Looks like it is not that hard after all i already tried this but apparently did something wrong because when i just tried again it did work :
DataColumn[] esl = new DataColumn[] { dt.Columns["Naam"] };
if (ds.Tables[0].PrimaryKey == null || ds.Tables[0].PrimaryKey == esl)
{
ds.Tables[0].PrimaryKey = new DataColumn[] { dt.Columns["Naam"] };
}
if (ds.Tables[0].PrimaryKey.Length == 0)
ds.Tables[0].PrimaryKey = new DataColumn[] { dt.Columns["Naam"] };
Related
Here i am using simple list and one of the ageto string column is null
I am check in linq query if value not found then to return null. But value cannot be null error is coming up
var list = new[]
{
new { AgeFrom = "0", AgeTo="24"},
new { AgeFrom = "70", AgeTo= (string)null}
}.ToList();
var result = from r in list
select new EmployeeDTO
{
//AgeFrom Column is int? in DTO
AgeFrom = Convert.ToInt32(r.AgeFrom),
//AgeTo Column is int? in DTO
AgeTo = Convert.ToInt32(r.AgeTo ?? null)
}
Try this:
AgeTo = String.IsNullOrEmpty(r.AgeTo) ? (int?)null : (int?)Convert.ToInt32(r.AgeTo);
Which makes your code:
var list = new[]
{
new { AgeFrom = "0", AgeTo="24"},
new { AgeFrom = "70", AgeTo= (string)null}
}.ToList();
var result = from r in list
select new EmployeeDTO
{
//AgeFrom Column is int? in DTO
AgeFrom = Convert.ToInt32(r.AgeFrom),
//AgeTo Column is int? in DTO
String.IsNullOrEmpty(r.AgeTo) ? (int?)null : (int?)Convert.ToInt32(r.AgeTo)
};
Convert.ToInt32 can not convert null to an integer, that will always throw an exception.
One option would be to change:
AgeTo = Convert.ToInt32(r.AgeTo ?? null)
to:
AgeTo = r.AgeTo != null ? Convert.ToInt32(r.AgeTo) : null
The statement r.AgeTo ?? null is an example of the null-coalescing operator, which, in your case, is essentially saying that if r.AgeTo is null, then use null instead. As this isn't what you were trying to achieve, you are in fact passing null into Convert.ToInt32, which is causing your error.
In my controller I have a method that receives a decimal value (id).
The objective of this method is to recover a list of old revisions from a database table containing work permits. Each record on this table has a WorkPermitID as a primary key and OldRevisionWorkPermitID referencing the ID of the previous version.
I have no problems when collecting the children IDs (old versions), but it raises an exception indicating that LINQ to Entities does not recognize .ToString() method.
What I'm doing wrong? I know that I need to do without converting to string (WorkPermitID is defined as numeric in the database), but I tried several ways with no success.
public ActionResult GetVersions(decimal id){
var model = new PermisosTrabajoModel();
List<string> ChildIDs = new List<string>();
var WP = OtWeb.WorkPermit.Single(q => q.WorkPermitID == id);
while (WP.OldRevisionWorkPermitID != null)
{
var child = WP.OldRevisionWorkPermitID;
ChildIDs.Add(child.ToString());
WP = OtWeb.WorkPermit.Single(q => q.WorkPermitID == child);
}
model.WPs = OtWeb.WorkPermit
.Where(q => q.DeptID == 1
&& ChildIDs.Contains(q.WorkPermitID.ToString())).ToList();
return View (model);
}
Solution1
If both of your fields are decimal... Don't use ToString(), and use a list of decimal
var model = new PermisosTrabajoModel();
var childIDs = new List<decimal>();
var WP = OtWeb.WorkPermit.Single(q => q.WorkPermitID == id);
while (WP.OldRevisionWorkPermitID != null)
{
childIDs.Add(WP.OldRevisionWorkPermitID);
WP = OtWeb.WorkPermit.Single(q => q.WorkPermitID == child);
}
model.WPs = OtWeb.WorkPermit
.Where(q => q.DeptID == 1
&& childIDs.Contains(q.WorkPermitID)).ToList();
Solution2
In linq2entities, you can use SqlFunctions.StringConvert instead of ToString() for a numeric value.
SqlFunctions.StringConvert(q.WorkPermitId)
instead of
q.WorkPermitID.ToString()
for example
While looking though some code of the project I'm working on, I've come across a pretty hefty method which does
the following:
public string DataField(int id, string fieldName)
{
var data = _dataRepository.Find(id);
if (data != null)
{
if (data.A == null)
{
data.A = fieldName;
_dataRepository.InsertOrUpdate(data);
return "A";
}
if (data.B == null)
{
data.B = fieldName;
_dataRepository.InsertOrUpdate(data);
return "B";
}
// keep going data.C through data.Z doing the exact same code
}
}
Obviously having 26 if statements just to determine if a property is null and then to update that property and do a database call is
probably very naive in implementation. What would be a better way of doing this unit of work?
Thankfully C# is able to inspect and assign class members dynamically, so one option would be to create a map list and iterate over that.
public string DataField(int id, string fieldName)
{
var data = _dataRepository.Find(id);
List<string> props = new List<string>();
props.Add("A");
props.Add("B");
props.Add("C");
if (data != null)
{
Type t = typeof(data).GetType();
foreach (String entry in props) {
PropertyInfo pi = t.GetProperty(entry);
if (pi.GetValue(data) == null) {
pi.SetValue(data, fieldName);
_dataRepository.InsertOrUpdate(data);
return entry;
}
}
}
}
You could just loop through all the character from 'A' to 'Z'. It gets difficult because you want to access an attribute of your 'data' object with the corresponding name, but that should (as far as I know) be possible through the C# reflection functionality.
While you get rid of the consecutive if-statements this still won't make your code nice :P
there is a fancy linq solution for your problem using reflection:
but as it was said before: your datastructure is not very well thought through
public String DataField(int id, string fieldName)
{
var data = new { Z = "test", B="asd"};
Type p = data.GetType();
var value = (from System.Reflection.PropertyInfo fi
in p.GetProperties().OrderBy((fi) => fi.Name)
where fi.Name.Length == 1 && fi.GetValue(data, null) != null
select fi.Name).FirstOrDefault();
return value;
}
ta taaaaaaaaa
like that you get the property but the update is not yet done.
var data = _dataRepository.Find(id);
If possible, you should use another DataType without those 26 properties. That new DataType should have 1 property and the Find method should return an instance of that new DataType; then, you could get rid of the 26 if in a more natural way.
To return "A", "B" ... "Z", you could use this:
return (char)65; //In this example this si an "A"
And work with some transformation from data.Value to a number between 65 and 90 (A to Z).
Since you always set the lowest alphabet field first and return, you can use an additional field in your class that tracks the first available field. For example, this can be an integer lowest_alphabet_unset and you'd update it whenever you set data.{X}:
Init:
lowest_alphabet_unset = 0;
In DataField:
lowest_alphabet_unset ++;
switch (lowest_alphabet_unset) {
case 1:
/* A is free */
/* do something */
return 'A';
[...]
case 7:
/* A through F taken */
data.G = fieldName;
_dataRepository.InsertOrUpdate(data);
return 'G';
[...]
}
N.B. -- do not use, if data is object rather that structure.
what comes to my mind is that, if A-Z are all same type, then you could theoretically access memory directly to check for non null values.
start = &data;
for (i = 0; i < 26; i++){
if ((typeof_elem) *(start + sizeof(elem)*i) != null){
*(start + sizeof(elem)*i) = fieldName;
return (char) (65 + i);
}
}
not tested but to give an idea ;)
I need to return a single instance of my viewmodel class from my repository in order to feed this into a strongly-typed view
In my repository, this works fine for a collection of viewmodel instances:
IEnumerable<PAWeb.Domain.Entities.Section> ISectionsRepository.GetSectionsByArea(int AreaId)
{
var _sections = from s in DataContext.Sections where s.AreaId == AreaId orderby s.Ordinal ascending select s;
return _sections.Select(x => new PAWeb.Domain.Entities.Section()
{
SectionId = x.SectionId,
Title = x.Title,
UrlTitle = x.UrlTitle,
NavTitle = x.NavTitle,
AreaId = x.AreaId,
Ordinal = x.Ordinal
}
);
}
But when I attempt to obtain a single entity, like this:
public PAWeb.Domain.Entities.Section GetSection(int SectionId)
{
var _section = from s in DataContext.Sections where s.SectionId == SectionId select s;
return _section.Select(x => new PAWeb.Domain.Entities.Section()
{
SectionId = x.SectionId,
Title = x.Title,
UrlTitle = x.UrlTitle,
NavTitle = x.NavTitle,
AreaId = x.AreaId,
Ordinal = x.Ordinal
}
);
}
I get
Error 1 Cannot implicitly convert type
'System.Linq.IQueryable<PAWeb.Domain.Entities.Section>' to
'PAWeb.Domain.Entities.Section'. An explicit conversion exists
(are you missing a cast?)"
This has got to be simple, but I'm new to c#, and I can't figure out the casting. I tried (PAWeb.Domain.Entities.Section) in various places, but no success. Can anyone help??
Your query is returning an IQueryable, which could have several items. For example, think of the difference between an Array or List of objects and a single object. It doesn't know how to convert the List to a single object, which one should it take? The first? The last?
You need to tell it specifically to only take one item.
e.g.
public PAWeb.Domain.Entities.Section GetSection(int SectionId)
{
var _section = from s in DataContext.Sections where s.SectionId == SectionId select s;
return _section.Select(x => new PAWeb.Domain.Entities.Section()
{
SectionId = x.SectionId,
Title = x.Title,
UrlTitle = x.UrlTitle,
NavTitle = x.NavTitle,
AreaId = x.AreaId,
Ordinal = x.Ordinal
}
).FirstOrDefault();
}
This will either return the first item, or null if there are no items that match your query. In your case that won't happen unless the table is empty since you don't have a where clause.
I am using SubSonic 3.0.0.3 along with the Linq T4 Templates. My ProjectRepository, for example, has the following two methods:
public int Add(Project item)
{
int result = 0;
ISqlQuery query = BuildInsertQuery(item);
if (query != null)
{
result = query.Execute();
}
return result;
}
private ISqlQuery BuildInsertQuery(Project item)
{
ITable tbl = FindTableByClassName();
Insert query = null;
if (tbl != null)
{
Dictionary<string, object> hashed = item.ToDictionary();
query = new Insert(_db.Provider).Into<Project>(tbl);
foreach (string key in hashed.Keys)
{
IColumn col = tbl.GetColumn(key);
if (col != null)
{
if (!col.AutoIncrement)
{
query.Value(key, hashed[key]);
}
}
}
}
return query;
}
Along with performing the insert (which works great), I'd really like to get the value of the auto-incrementing ProjectId column. For the record, this column is both the primary key and identity column. Is there perhaps a way to append "SELECT SCOPE_IDENTITY();" to the query or maybe there's an entirely different approach which I should try?
You can do this with the ActiveRecord templates which does all of the wiring above for you (and also has built-in testing). In your scenario, the Add method would have one line: Project.Add() and it would return the new id.
For your needs, you can try this:
var cmd=query.GetCommand();
cmd.CommandSql+=";SELECT SCOPE_IDENTITY() as newid";
var newID=query.Provider.ExecuteScalar(cmd);
That should work..
*Edit - you can create an ExtensionMethod for this on ISqlQuery too, to save some writing...