As I understand it, the following code should generate a query containing only the RouteId, RouteNo, and ShipId
var tow = (from t in _context.AllTowData
where t.RouteId == id
orderby t.RouteNo descending
select new TowDefaults {
Id = t.RouteId,
TowNo = t.RouteNo,
ShipId = t.ShipId,
LastTow = t.RouteNo
})
.FirstOrDefault();
However, I get:
SELECT v.route_id, v.route_no, v.tow_id, v.analysis_complete, v.checks_complete, v.cpr_id, v.date_created, v.date_last_modified, v.factor, v.fromportname, v.instrument_data_file, v.instrument_id, v.internal_number, v.mastername, v.message, v.miles_per_division, v.month, v.number_of_samples, v.number_of_samples_analysed_fully, v.prop_setting, v.route_status, v.sampled_mileage, v.serial_no_per_calendar_month, v.ship_speed, v.silk_reading_end, v.silk_reading_start, v.toportname, v.tow_mileage, v.validity, v.year
FROM view_all_tow_data AS v
WHERE v.route_id = '#__id_0'
ORDER BY v.route_no DESC
LIMIT 1
That's every column except the explicitly requested ShipId! What am I doing wrong?
This happens using both a SQL Server and a PostGres database
The property ShipIdis not mapped, either by a [NotMapped] annotation or a mapping instruction. As far as EF is concerned, the property doesn't exist. This has two effects:
EF "notices" that there's an unknown part the final Select and it switches to client-side evaluation (because it's a final Select). Which means: it translates the query before the Select into SQL which doesn't contain the ShipId column, executes it, and materializes full AllTowData entities.
It evaluates the Select client-side and returns the requested TowDefaults objects in which ShipId has its default value, or any value you initialize in C# code, but nothing from the database.
You can verify this by checking _context.AllTowData.Local after the query: it will contain all AllTowData entities that pass the filter.
From your question it's impossible to tell what you should do. Maybe you can map the property to a column in the view. If not, you should remove it from the LINQ query. Using it in LINQ anywhere but in a final Select will cause a runtime exception.
Related
I am trying to access a table in my Secondary DB whose name I am obtaining from my Primary DB. My difficulty is to pass the "DB-Name" as a parameter into my secondary query, (BTW I am using MyBatis annotation based Mappers).
This is my Mapper
#SelectProvider(type = DealerQueryBuilder.class, method = "retrieveDealerListQuery")
#Results({
#Result(property="dealerID", column="frm_dealer_master_id"),
#Result(property="dealerTypeID", column="frm_dealer_type_id", one=#One(select="retrieveDealerTypeDAO")),
#Result(property="dealerName", column="frm_dealer_name")
})
public List<Dealer> retrieveDealerListDAO(#Param("firmDBName") String firmDBName);
#Select("SELECT * from ${firmDBName}.frm_dealer_type where frm_dealer_type_id=#{frm_dealer_type_id}")
#Results({
#Result(property="dealerTypeID", column="frm_dealer_type_id"),
#Result(property="dealerType", column="frm_dealer_type")
})
public DealerType retrieveDealerTypeDAO(#Param("firmDBName") String firmDBName, #Param("frm_dealer_type_id") int frm_dealer_type_id);
The firmDBName I have is obtained from my "Primary DB".
If I omit ${firmDBName} in my second query, the query is trying to access my Primary Database and throws out table "PrimaryDB.frm_dealer_type" not found. So it is basically trying to search for a table named "frm_dealer_type" in my Primary DB.
If I try to re-write the #Result like
#Result(property="dealerTypeID", column="firmDBName=firmDBName, frm_dealer_type_id=frm_dealer_type_id", one=#One(select="retrieveDealerTypeDAO")),
It throws an error that Column"firmDBName" does not exist.
Changing ${firmDBName} to #{firmDBName} also did not help.
I did refer to this blog - here
I want a solution to pass my parameter firmDBName from my primary query into secondary query.
The limitation here is that your column must be returned by the first #SELECT.
If you look at the test case here you will see that parent_xxx values returned by the first Select.
Your DealerQueryBuilder must select firmDBName as a return value and your column must map the name of the return column to that.
Your column definition is always wrong, it should be:
{frm_dealer_type_id=frm_dealer_type_id,firmDBName=firmDBName} or whatever it was returned as from your first select.
Again you can refer to the test case I have above as well as the documentation here http://www.mybatis.org/mybatis-3/sqlmap-xml.html#Nested_Select_for_Association
I have got a BaseEntity class which contains a, byte array called stamp, id and state, which every Entity inherits from I am mapping the stamp to
Property(t => t.Stamp).IsRequired().IsRowVersion();
this is set in BaseEntityConfiguration
which is set like this
public BaseEntityConfiguration<T> : EntityTypeConfiguration<T> where T :B aseEntity
The mapping is done like this
var baseMapConfiguration = new BaseEntityConfiguration<EntityA>();
modelBuilder.Configurations.Add(baseMapConfiguration);
var entityAMap = new EntityAMap(baseMapConfiguration);
The database has Stamp ROWVERSION NOT NULL; on the Table EntityA
I have code that handles DbUpdateConcurrencyException but this does not get caught even though the stamps are different
Also there is no where clause on with the Stamp field which I would expected
SELECT
[Extent1].[Id] AS [Id],
[Extent1].[LastModified] AS [LastModified],
[Extent1].[CreatedDate] AS [CreatedDate],
[Extent1].[Stamp] AS [Stamp]
FROM [dbo].[EntityA] AS [Extent1]
As you seen no where statement I have also tried it from the with a normal mapping set up but still get the same result
**I have found the problem EF is getting the latest Rowversion instead of the passed in one, How can I stop this. **
if (!EntityA.Stamp.Equals(orignal.Stamp))
{
ctx.Entry(orignal).OriginalValues["Stamp"] = xmlFile.Stamp;
}
I was missing these line of codes from the DAL, this is stop EF putting the current stamp as the search criteria.
In the following example, we insert an entity called taskinstance to our context. we have a foreign key FK_Contract that we set at 2.
entity.FK_Contract = 2;
context.TaskInstances.AddObject(entity);
The query generated by entity framework is a simple insert. (everything is fine)
However, the following query works differently.
int contractId = context.Contracts.Where((T) => T.Name == contractName).Single().Id;
entity.FK_Contract = contractId;
context.TaskInstances.AddObject(entity);
In the trace created by entity framework we see without surprise the query selecting the Id according a contractName but we also see an extra request looking like:
select id,... from [TaskInstances] WHERE [Extent1].[FK_Task] = #contractId
This extra query leads to many problems, especially when we work with a foreign table with millions of record. The network goes down!
Therefore we 'd like to figure out the purpose of this extra query and the way to make it disappear.
It looks like the extra query is populating a collection of tasks on the returned Contract object. Try projecting just the column you want:
int contractId = context.Contracts
.Where(T => T.Name == contractName)
.Select(T => T.Id)
.Single();
I have a statement:
var items = from e in db.Elements
join a in db.LookUp
on e.ID equals a.ElementID
where e.Something == something
select new Element
{
ID = e.ID,
LookUpID = a.ID
// some other data get populated here as well
};
As you can see, all I need is a collection of Element objects with data from both tables - Elements and LookUp. This works fine. But then I need to know the number of elements selected:
int count = items.Count();
... this call throws System.NotSupportedException:
"The entity or complex type 'Database.Element' cannot be constructed in a LINQ to Entities query."
How am I supposed to select values from multiple tables into one object in Entity Framework? Thanks for any help!
You are not allowed to create an Entity class in your projection, you have to either project to a new class or an anonymous type
select new
{
ID = e.ID,
LookUpID = a.ID
// some other data get populated here as well
};
Your code doesn't work at all. The part you think worked has never been executed. The first time you executed it was when you called Count.
As exception says you cannot construct mapped entity in projection. Projection can be made only to anonymous or non mapped types. Also it is not clear why you even need this. If your class is correctly mapped you should simply call:
var items = from e in db.Elements
where e.Something == something
select e;
If LookupID is mapped property of your Element class it will be filled. If it is not mapped property you will not be able to load it with single query to Element.
I have a table AccountSecurity which is a many-to-many table that relates Account entities and Securities. When I write the query below it returns all Securities that satisfy the where clause. However each Security instance in the list no longer has the reference to the AccountSecurity it came from. So when I do list[0].AccountSecurity it is empty. Is there anyway to include that information? I know I can rewrite the query to return AccountSecurities instead and use .Include("Security") on that, but I wonder if it can be done another way.
var list = (from acctSec in base.context.AccountSecurities
where acctSec.AccountId == accountId
select acctSec.Security).ToList();
UPDATE
Of course if I do two queries the graph gets populated properly, there has to be a way to do this in one shot.
var securities = (from acctSec in base.context.AccountSecurities
where acctSec.AccountId == accountId
select acctSec.Security).ToList();
//this query populates the AccountSecurities references within Security instances returned by query above
var xref = (from acctSec in base.context.AccountSecurities
where acctSec.AccountId == accountId
select acctSec).ToList();
var list = (from sec in base.context.Securities
.Include("AccountSecurity")
where sec.AccountSecurities.Any(as => as.AccountId == accountId)
select sec).ToList();
Try this:
var list = (from acctSec in base.context.AccountSecurities.Include("Security")
where acctSec.AccountId == accountId
select acctSec).ToList();
Then simply use the Security property as needed, and since it's read at the same time AccountSecurities is (single SQL with join), it will be very efficient.