Develop Reference

how to use an expression in a select clause

consider the following pseudp code
Expression<Func<E,Datetime?>> expr =
e => (e.d1 ?? e.Rel.d1) ?? e.d2;
var q = myContext.E_DbSet.Select(x => new someDeclaredType {
Id = x.Id,
V = expr
});
=> CS0029 Cannot implicitly convert type 'System.Linq.Expressions.Expression>' to 'System.DateTime?'
if I try with compile
Expression<Func<E,Datetime?>> expr =
(e => (e.d1 ?? e.Rel.d1) ?? e.d2).Compile();
var q = myContext.E_DbSet.Select(x => new someDeclaredType {
Id = x.Id,
V = expr(x)
});
=> NotSupportedException: node type 'Invoke' of LINQ expression is not suported in LINQ to Entities.
I read Invoke an Expression in a Select statement - LINQ to Entity Framework. But this is not my exact case. I need to include an existing expression into my select clause. This expression comes as the result of a function call. So I must use expr in my select clause.
How can it be done ?

Maybe something like this:
Expression<Func<E,someDeclaredType>> expr =
e => new someDeclaredType()
{
Id = e.Id,
V = (e.d1 ?? e.Rel.d1) ?? e.d2
};
var q = myContext.E_DbSet.Select(expr);

I finally found a way:
Expression<Func<E,Datetime?>> expr =
e => (e.d1 ?? e.Rel.d1) ?? e.d2;
Expression<Func<E,someDeclaredType>> sel =
x => new someDeclaredType {
Id = x.Id,
V = expr.Compile()(x)
};
var q = myContext.E_DbSet.Select(sel.Compile());
another coding is (from #Anthony):
Expression<Func<E, someDeclaredType>> sel =
e => new someDeclaredType()
{
Id = e.Id,
V = expr.Compile()(e)
};
q = Files.Select(sel.Compile());
by the sample: dotnetfiddle
Please not that the code is designed for linq to entities. It may fire exception in linq to object due to Rel = null.

Cannot convert Linq to SQL

So for a assignement I got I have to convert the data I get through an API into a object and save that object in the database. Since the object doesn't have a any property that is unique there are multiple primary key columns in my database.
So what I basically have to do is a 'merge' from to my database so if data has been changed to a update if data is new do an insert. For some reason one my linq queries for this is giving an error.
My database:
My Code:
public void Insert(List<MEDSU1> medsu1s)
{
var keys = medsu1s.Select(y => new { SUPP = y.S1SUPP?.Trim() ?? null, COMP = y.S1COMP?.Trim() ??null }).ToList();
List<MEDSU1> medusFromSql = MediusDataContext.MEDSU1s.Where(y =>
keys.Any(z => z.SUPP == y.S1SUPP && z.COMP == y.S1COMP)).ToList();
var toUpdate = from medsu1org in MediusDataContext.MEDSU1s
join sqlkeys in medusFromSql
on new
{
aa = medsu1org.S1COMP,
bb = medsu1org.S1SUPP
}
equals
new
{
aa = sqlkeys.S1COMP,
bb = sqlkeys.S1SUPP
}
select new
{
sql = medsu1org,
obj = sqlkeys,
};
toUpdate.ToList().ForEach(y =>
{
y.obj.S1COMP= y.sql.S1COMP;
y.obj.S1SUPP = y.sql.S1SUPP;
y.obj.S1SUNA = y.sql.S1SUNA;
y.obj.S1BAAC = y.sql.S1BAAC;
y.obj.S1VATN = y.sql.S1VATN;
y.obj.S1COUN = y.sql.S1COUN;
y.obj.S1PREF = y.sql.S1PREF;
y.obj.S1TAXD = y.sql.S1TAXD;
y.obj.S1CURR = y.sql.S1CURR;
y.obj.S1TYPE = y.sql.S1TYPE;
y.obj.S1ACNR = y.sql.S1ACNR;
y.obj.S1ACNM = y.sql.S1ACNM;
y.obj.S1EINV = y.sql.S1EINV;
y.obj.S1DLAY = y.sql.S1DLAY;
y.obj.S1TERM = y.sql.S1TERM;
y.obj.S1PYEE = y.sql.S1PYEE;
});
var toInsert = medsu1s.Except(toUpdate.Select(y => y.obj)).ToList();
MediusDataContext.MEDSU1s.InsertAllOnSubmit(toInsert);
MediusDataContext.SubmitChanges();
}
The part of the code that is giving me the error is the:
var keys = medsu1s.Select(y => new { SUPP = y.S1SUPP?.Trim() ?? null, COMP = y.S1COMP?.Trim() ??null }).ToList();
List<MEDSU1> medusFromSql = MediusDataContext.MEDSU1s.Where(y =>
keys.Any(z => z.SUPP == y.S1SUPP && z.COMP == y.S1COMP)).ToList();
I think it has to do with me using .Any incorrectly and converting it to a List but i dont know to fix it. Can someone explain me what I'm doing wrong?
ERROR im getting : "Local sequence cannot be used in LINQ to SQL implementations of query operators except the Contains operator."

Since you're dealing with a compound key you'll have to create a query that basically looks like
Select *
From MEDSU1s
Where (S1SUPP == #S1SUPP1 && S1COMP == #S1COMP1)
OR (S1SUPP == #S1SUPP2 && S1COMP == #S1COMP2)
OR ....
To do that with Linq you'd have to build the expression procedurally. Note that I'm assuming the columns are both strings, so change the type of them as needed. Also I have no good way of testing this out but hopefully this can get you started towards a solution.
var queryableData = MediusDataContext.MEDSU1s;
var table = Expression.Parameter(typeof(MEDSU1s), "x");
var suppCol = Expression.Property(table, typeof(string), "S1SUPP");
var compCol = Expression.Property(table, typeof(string), "S1COMP");
Expression condition = Expression.Equal(Expression.Constant(1), Expression.Constant(0));
foreach (var x in keys)
{
var key1 = Expression.Equal(suppCol, Expression.Constant(x.SUPP));
var key2 = Expression.Equal(compCol, Expression.Constant(x.COMP));
var both = Expression.AndAlso(key1, key2);
condition = Expression.OrElse(condition, both);
}
var whereExpression = Expression.Call(
typeof(Queryable),
"Where",
new Type[] { queryableData.ElementType },
queryableData.Expression,
Expression.Lambda<Func<MEDSU1s, bool>>(
condition,
new ParameterExpression[] { table }));
var medusFromSql = queryableData.Provider.CreateQuery<MEDSU1s>(whereExpression).ToList();

How do you reuse mapping functions on Nested entities in Entity Framework?

I have seen multiple questions that are similar to this one but I think my case is slightly different. I'm using EF6 to query the database and I'm using data projection for better queries.
Given that performance is very important on this project I have to make sure to just read the actual fields that I will use so I have very similar queries that are different for just a few fields as I have done this I have noticed repetition of the code so I'm been thinking on how to reuse code this is currently what I Have:
public static IEnumerable<FundWithReturns> GetSimpleFunds(this DbSet<Fund> funds, IEnumerable<int> fundsId)
{
IQueryable<Fund> query = GetFundsQuery(funds, fundsId);
var results = query
.Select(f => new FundWithReturns
{
Category = f.Category,
ExpenseRatio = f.ExpenseRatio,
FundId = f.FundId,
Name = f.Name,
LatestPrice = f.LatestPrice,
DailyReturns = f.FundDailyReturns
.Where(dr => dr.AdjustedValue != null)
.OrderByDescending(dr => dr.CloseDate)
.Select(dr => new DailyReturnPrice
{
CloseDate = dr.CloseDate,
Value = dr.AdjustedValue.Value,
}),
Returns = f.Returns.Select(r => new ReturnValues
{
Daily = r.AdjDaily,
FiveYear = r.AdjFiveYear,
MTD = r.AdjMTD,
OneYear = r.AdjOneYear,
QTD = r.AdjQTD,
SixMonth = r.AdjSixMonth,
ThreeYear = r.AdjThreeYear,
YTD = r.AdjYTD
}).FirstOrDefault()
})
.ToList();
foreach (var result in results)
{
result.DailyReturns = result.DailyReturns.ConvertClosingPricesToDailyReturns();
}
return results;
}
public static IEnumerable<FundListVm> GetFundListVm(this DbSet<Fund> funds, string type)
{
return funds
.Where(f => f.StatusCode == MetisDataObjectStatusCodes.ACTIVE
&& f.Type == type)
.Select(f => new FundListVm
{
Category = f.Category,
Name = f.Name,
Symbol = f.Symbol,
Yield = f.Yield,
ExpenseRatio = f.ExpenseRatio,
LatestDate = f.LatestDate,
Returns = f.Returns.Select(r => new ReturnValues
{
Daily = r.AdjDaily,
FiveYear = r.AdjFiveYear,
MTD = r.AdjMTD,
OneYear = r.AdjOneYear,
QTD = r.AdjQTD,
SixMonth = r.AdjSixMonth,
ThreeYear = r.AdjThreeYear,
YTD = r.AdjYTD
}).FirstOrDefault()
}).OrderBy(f=>f.Symbol).Take(30).ToList();
}
I'm trying to reuse the part where I map the f.Returns so I tried created a Func<> like the following:
private static Func<Return, ReturnValues> MapToReturnValues = r => new ReturnValues
{
Daily = r.AdjDaily,
FiveYear = r.AdjFiveYear,
MTD = r.AdjMTD,
OneYear = r.AdjOneYear,
QTD = r.AdjQTD,
SixMonth = r.AdjSixMonth,
ThreeYear = r.AdjThreeYear,
YTD = r.AdjYTD
};
and then use like this:
public static IEnumerable<FundListVm> GetFundListVm(this DbSet<Fund> funds, string type)
{
return funds
.Where(f => f.StatusCode == MetisDataObjectStatusCodes.ACTIVE
&& f.Type == type)
.Select(f => new FundListVm
{
Category = f.Category,
Name = f.Name,
Symbol = f.Symbol,
Yield = f.Yield,
ExpenseRatio = f.ExpenseRatio,
LatestDate = f.LatestDate,
Returns = f.Returns.Select(MapToReturnValues).FirstOrDefault()
}).OrderBy(f=>f.Symbol).Take(30).ToList();
}
The compiler is ok with it but at runtime, it crashes and says: Internal .NET Framework Data Provider error 1025
I tried to convert the Func into Expression like I read on some questions and then using compile() but It didn't work using AsEnumerable is also not an option because It will query all the fields first which is what I want to avoid.
Am I trying something not possible?
Thank you for your time.

It definitely needs to be Expression<Func<...>>. But instead of using Compile() method (not supported), you can resolve the compile time error using the AsQueryable() method which is perfectly supported (in EF6, the trick doesn't work in current EF Core).
Given the modified definition
private static Expression<Func<Return, ReturnValues>> MapToReturnValues =
r => new ReturnValues { ... };
the sample usage would be
Returns = f.Returns.AsQueryable().Select(MapToReturnValues).FirstOrDefault()

Select Statements in LINQ Efficiency

For code shown below, I'm wondering is there a more efficient way of assigning the Status and Types in the select statement? There is no relationship between the contract and the statuses/types as the contract items are coming from an API call and the statuses/types are from a local database.
The part in question is
Status = statuses.FirstOrDefault(y => y.StatusId == x.StatusId)
Type = types.FirstOrDefault(y => y.TypeId == x.TypeId)
Is there a better way of assigning these?
var statuses = this.StatusRepository.GetActiveStatuses().ToList();
var types = this.TypeRepository.GetActiveTypes().ToList();
var contracts = this.ContractApi.GetCurrentContracts().Select(x => new ContractItem {
Id = x.Id,
Name = x.Name,
Status = statuses.FirstOrDefault(y => y.StatusId == x.StatusId) ?? Status.Empty(),
Type = types.FirstOrDefault(y => y.TypeId == x.TypeId) ?? Type.Empty()
});

For better performance you should use a dictionary or lookup:
var statuses = this.StatusRepository.GetActiveStatuses().ToLookup(x => x.StatusId);
var types = this.TypeRepository.GetActiveTypes().ToLookup(x => x.TypeId);
var emptyStatus = Status.Empty();
var emptyType = Type.Empty();
var contracts = this.ContractApi.GetCurrentContracts()
.Select(x => new ContractItem {
Id = x.Id,
Name = x.Name,
Status = statuses[x.StatusId].DefaultIfEmpty(emptyStatus).First(),
Type = types[x.TypeId].DefaultIfEmpty(emptyType).First()
});
The lookup is more readable because it enables to use DefaultIfEmpty

If you know they will exist in your local database you could store them in a Dictionary like;
var statusDict = this.StatusRepository.GetActiveStatuses().ToDictionary(s => s.StatusId);
....
Status = statusDict[x.StatusId]

Check for missing elements while using LINQ to XML

I am trying get data from the xml. Below is the code which
gets data from the XDocument and return list<t>.
However, p.Element("Sponsor") can sometimes be null. How can I check for the null values
var atClauseList = doc.Descendants(CLAUSE_GROUP_TAG).Descendants(AT_CLAUSE_TAG).Select(p => new AtClause()
{
ClauseNumber = (string)p.Element("Number"),
Sponsors = p.Element("Sponsor").Elements(SPONSOR_TAG).Select(y => y.Value)
.ToList(),
Page = p.Element("Sponsor").Element("aItem").Element("AmendText").Element("Page").ElementValueNull(),
Line = p.Element("Sponsor").Element("aItem").Element("AmendText").Element("Line").ElementValueNull(),
LineText = p.Element("Sponsor").Element("aItem").Element("AmendText").Nodes().OfType<XText>().FirstOrDefault().XTextValueNull(),
ItalicText = p.Element("Sponsor").Element("aItem").Element("AmendText").Element("Italic").ElementValueNull(),
ParaList = p.Element("Sponsor").Element("aItem").Element("AmendText").Elements("Para").Select(L => new Para
{
ParaText = (string)L,
Number = ((System.Xml.Linq.XElement)(L)).AttributeValueNull("Number"),
Quote = ((System.Xml.Linq.XElement)(L)).AttributeValueNull("Quote"),
}
).ToList()
}).ToList();

move your code out of an object initializer, and add some logic to it:
var atClauseList = new List<AtClause>();
foreach(var item in doc.Descendants(CLAUSE_GROUP_TAG).Descendants(AT_CLAUSE_TAG))
{
var atClause = new AtClause();
atClause.ClauseNumber = (string)item.Element("Number");
var sponsor = item.Element("Sponsor");
if (sponsor != null)
{
atClause.Sponsors = sponsor.Elements(SPONSOR_TAG).Select(y => y.Value).ToList();
atClause.Page = sponsor.Element("aItem").Element("AmendText").Element("Page").ElementValueNull();
atClause.Line = sponsor.Element("aItem").Element("AmendText").Element("Line").ElementValueNull();
atClause.LineText = sponsor.Element("aItem").Element("AmendText").Nodes().OfType<XText>().FirstOrDefault().XTextValueNull();
atClause.ItalicText = sponsor.Element("aItem").Element("AmendText").Element("Italic").ElementValueNull();
atClause.ParaList = sponsor.Element("aItem").Element("AmendText").Elements("Para").Select(L => new Para
{
ParaText = (string)L,
Number = ((System.Xml.Linq.XElement)(L)).AttributeValueNull("Number"),
Quote = ((System.Xml.Linq.XElement)(L)).AttributeValueNull("Quote"),
}).ToList();
atClauseList.Add(atClause);
}

You can use sequences rather than leaving the IEnumerable immediately:
var value = (string)p.Elements("Sponsor")
.Elements("aItem")
.Elements("AmendText")
.Elements("Page")
.SingleOrDefault()