I create a complex search query in native SQL. It's basically something like this:
SELECT ID FROM t_Product WHERE Name LIKE #criteria
SELECT publisher, count(*) as number FROM t_Product GROUP BY publisher
It has 2 SELECT statements and I want it to be sent to DB server in one round trip.
But I can't figure out how to achieve this in Nhibernate.
I considered following options but none seems to work
Use CreateMultiQuery, but this only accept HQL, not native SQL
Use CreateSQLQuery, but call to List() only return result for the first SELECT statement
Moving to a stored procedure is not an option since the whole SQL is very dynamic.
We still use Nhibernate 1.2 thus new features in later version couldn't be used either.
Advice are welcome.
Not possible using NH version 1.2
Futures was released in version 2.1 which allows you to do exactly this.
e.g.
var blogs = s.CreateCriteria<Invoice>()
.SetMaxResults(30)
.Future<Invoice>();
var countOfInvoices = s.CreateCriteria<Invoice>()
.SetProjection(Projections.Count(Projections.Id()))
.FutureValue<int>();
So you are going to either upgrade, fall back to ADO.NET and use multiple recordsets or live with what you have! Sorry!
This is really going to be scenario-specific, but if you're stuck with NH Version 1.2, and eliminating the round-trip is your goal, you could consider rewriting this as a single query using a sub-select.
Something along the lines of:
SELECT publisher, count(*) as number,
(SELECT ID FROM t_Product WHERE Name LIKE #criteria) As theId
FROM t_Product GROUP BY publisher
Would work if your subquery only returned a single value.
I don't think that it is possible, because both queries are SELECTs.
You may try a semicolon after the first query, and two line feeds between them, this is required for some databases. I successfully run query-scripts like this. If it runs, use a debugger to see what you get back ...
If this doesn't work, you need separate round trips or switch to HQL / Criteria.
You can use MultiQuery "Hack" like this:
The procudure:
CREATE PROCEDURE [dbo].[proc_Name]
AS BEGIN
SELECT * FROM t_Question where ...
SELECT * FROM t_Question where ........
END
The NHibernate Query Code:
public void ProcdureMultiTableQuery()
{
var session = Session;
var procSQLQuery = session.CreateSQLQuery("exec [proc_Name] ?,?");// prcodure returns two table
procSQLQuery.SetParameter(0, userId);
procSQLQuery.SetParameter(1, page);
procSQLQuery.AddEntity(typeof(Question));
var multiResults = session.CreateMultiQuery()
.Add(procSQLQuery)
// More table your procedure returns,more empty SQL query you should add
.Add(session.CreateSQLQuery(" ").AddEntity(typeof(Question))) // the second table returns Question Model
.List();
if (multiResults == null || multiResults.Count == 0)
{
return;
}
if (multiResults.Count != 2)
{
return;
}
var questions1 = ConvertObjectsToArray<Question>((System.Collections.IList)multiResults[0]);
var questions2 = ConvertObjectsToArray<Question>((System.Collections.IList)multiResults[1]);
}
static T[] ConvertObjectsToArray<T>(System.Collections.IList objects)
{
if (objects == null || objects.Count == 0)
{
return null;
}
var array = new T[objects.Count];
for (int i = 0; i < array.Length; i++)
{
array[i] = (T)objects[i];
}
return array;
}
I'm using entity framework to connect with the database. I've one little problem:
I've one table which have one varbinary(MAX) column(with filestream).
I'm using SQL request to manage the "Data" part, but EF for the rest(metadata of the file).
I've one code which has to get all files id, filename, guid, modification date, ... of a file. This doesn't need at all the "Data" field.
Is there a way to retrieve a List but without this column filled?
Something like
context.Files.Where(f=>f.xyz).Exclude(f=>f.Data).ToList();
??
I know I can create anonymous objects, but I need to transmit the result to a method, so no anonymous methods. And I don't want to put this in a list of anonymous type, and then create a list of my non-anonymous type(File).
The goal is to avoid this:
using(RsSolutionsEntities context = new RsSolutionsEntities())
{
var file = context.Files
.Where(f => f.Id == idFile)
.Select(f => new {
f.Id, f.MimeType, f.Size, f.FileName, f.DataType,
f.DateModification, f.FileId
}).FirstOrDefault();
return new File() {
DataType = file.DataType, DateModification = file.DateModification,
FileId = file.FileId, FileName = file.FileName, Id = file.Id,
MimeType = file.MimeType, Size = file.Size
};
}
(I'm using here the anonymous type because otherwise you will get a NotSupportedException: The entity or complex type 'ProjectName.File' cannot be constructed in a LINQ to Entities query.)
(e.g. this code throw the previous exception:
File file2 = context.Files.Where(f => f.Id == idFile)
.Select(f => new File() {Id = f.Id, DataType = f.DataType}).FirstOrDefault();
and "File" is the type I get with a context.Files.ToList(). This is the good class:
using File = MyProjectNamespace.Common.Data.DataModel.File;
File is a known class of my EF datacontext:
public ObjectSet<File> Files
{
get { return _files ?? (_files = CreateObjectSet<File>("Files")); }
}
private ObjectSet<File> _files;
Is there a way to retrieve a List but without this column filled?
Not without projection which you want to avoid. If the column is mapped it is natural part of your entity. Entity without this column is not complete - it is different data set = projection.
I'm using here the anonymous type because otherwise you will get a
NotSupportedException: The entity or complex type 'ProjectName.File'
cannot be constructed in a LINQ to Entities query.
As exception says you cannot project to mapped entity. I mentioned reason above - projection make different data set and EF don't like "partial entities".
Error 16 Error 3023: Problem in mapping fragments starting at line
2717:Column Files.Data in table Files must be mapped: It has no
default value and is not nullable.
It is not enough to delete property from designer. You must open EDMX as XML and delete column from SSDL as well which will make your model very fragile (each update from database will put your column back). If you don't want to map the column you should use database view without the column and map the view instead of the table but you will not be able to insert data.
As a workaround to all your problems use table splitting and separate the problematic binary column to another entity with 1 : 1 relation to your main File entity.
I'd do something like this:
var result = from thing in dbContext.Things
select new Thing {
PropertyA = thing.PropertyA,
Another = thing.Another
// and so on, skipping the VarBinary(MAX) property
};
Where Thing is your entity that EF knows how to materialize. The resulting SQL statement shouldn't include the large column in its result set, since it's not needed in the query.
EDIT: From your edits, you get the error NotSupportedException: The entity or complex type 'ProjectName.File' cannot be constructed in a LINQ to Entities query. because you haven't mapped that class as an entity. You can't include objects in LINQ to Entities queries that EF doesn't know about and expect it to generate appropriate SQL statements.
You can map another type that excludes the VarBinary(MAX) column in its definition or use the code above.
you can do this:
var files = dbContext.Database.SqlQuery<File>("select FileId, DataType, MimeType from Files");
or this:
var files = objectContext.ExecuteStoreQuery<File>("select FileId, DataType, MimeType from Files");
depending on your version of EF
I had this requirement because I have a Document entity which has a Content field with the content of the file, i.e. some 100MB in size, and I have a Search function that I wanted to return the rest of the columns.
I chose to use projection:
IQueryable<Document> results = dbContext.Documents.Include(o => o.UploadedBy).Select(o => new {
Content = (string)null,
ContentType = o.ContentType,
DocumentTypeId = o.DocumentTypeId,
FileName = o.FileName,
Id = o.Id,
// etc. even with related entities here like:
UploadedBy = o.UploadedBy
});
Then my WebApi controller passes this results object to a common Pagination function, which applies a .Skip, .Take and a .ToList.
This means that when the query gets executed, it doesn't access the Content column, so the 100MB data is not being touched, and the query is as fast as you'd want/expect it to be.
Next, I cast it back to my DTO class, which in this case is pretty much exactly the same as the entity class, so this might not be a step you need to implement, but it's follows my typical WebApi coding pattern, so:
var dtos = paginated.Select(o => new DocumentDTO
{
Content = o.Content,
ContentType = o.ContentType,
DocumentTypeId = o.DocumentTypeId,
FileName = o.FileName,
Id = o.Id,
UploadedBy = o.UploadedBy == null ? null : ModelFactory.Create(o.UploadedBy)
});
Then I return the DTO list:
return Ok(dtos);
So it uses projection, which might not fit the original poster's requirements, but if you're using DTO classes, you're converting anyway. You could just as easily do the following to return them as your actual entities:
var dtos = paginated.Select(o => new Document
{
Content = o.Content,
ContentType = o.ContentType,
DocumentTypeId = o.DocumentTypeId,
//...
Just a few extra steps but this is working nicely for me.
For EF Core 2
I implemented a solution like this:
var files = context.Files.AsNoTracking()
.IgnoreProperty(f => f.Report)
.ToList();
The base idea is to turn for example this query:
SELECT [f].[Id], [f].[Report], [f].[CreationDate]
FROM [File] AS [f]
into this:
SELECT [f].[Id], '' as [Report], [f].[CreationDate]
FROM [File] AS [f]
you can see the full source code in here:
https://github.com/aspnet/EntityFrameworkCore/issues/1387#issuecomment-495630292
I'd like to share my attempts to workaround this problem in case somebody else is in the same situation.
I started with what Jeremy Danyow suggested, which to me is the less painful option.
// You need to include all fields in the query, just make null the ones you don't want.
var results = context.Database.SqlQuery<myEntity>("SELECT Field1, Field2, Field3, HugeField4 = NULL, Field5 FROM TableName");
In my case, I needed a IQueryable<> result object so I added AsQueryable() at the end. This of course let me add calls to .Where, .Take, and the other commands we all know, and they worked fine. But there's a caveat:
The normal code (basically context.myEntity.AsQueryable()) returned a System.Data.Entity.DbSet<Data.DataModel.myEntity>, while this approach returned System.Linq.EnumerableQuery<Data.DataModel.myEntity>.
Apparently this means that my custom query gets executed "as is" as soon as needed and the filtering I added later is done afterwards and not in the database.
Therefore I tried to mimic Entity Framework's object by using the exact query EF creates, even with those [Extent1] aliases, but it didn't work. When analyzing the resulting object, its query ended like
FROM [dbo].[TableName] AS [Extent1].Where(c => ...
instead of the expected
FROM [dbo].[TableName] AS [Extent1] WHERE ([Extent1]...
Anyway, this works, and as long as the table is not huge, this method will be fast enough. Otherwise you have no option than to manually add the conditions by concatenating strings, like classic dynamic SQL. A very basic example in case you don't know what I'm talking about:
string query = "SELECT Field1, Field2, Field3, HugeField4 = NULL, Field5 FROM TableName";
if (parameterId.HasValue)
query += " WHERE Field1 = " + parameterId.Value.ToString();
var results = context.Database.SqlQuery<myEntity>(query);
In case your method sometimes needs this field, you can add a bool parameter and then do something like this:
IQueryable<myEntity> results;
if (excludeBigData)
results = context.Database.SqlQuery<myEntity>("SELECT Field1, Field2, Field3, HugeField4 = NULL, Field5 FROM TableName").AsQueryable();
else
results = context.myEntity.AsQueryable();
If anyone manages to make the Linq extensions work properly like if it was the original EF object, please comment so I can update the answer.
I'm using here the anonymous type because otherwise you will get a
NotSupportedException: The entity or complex type 'ProjectName.File'
cannot be constructed in a LINQ to Entities query.
var file = context.Files
.Where(f => f.Id == idFile)
.FirstOrDefault() // You need to exeucte the query if you want to reuse the type
.Select(f => new {
f.Id, f.MimeType, f.Size, f.FileName, f.DataType,
f.DateModification, f.FileId
}).FirstOrDefault();
And also its not a bad practice to de-normalize the table into further, i.e one with metadata and one with payload to avoid projection. Projection would work, the only issue is, need to edit any time a new column is added to the table.
I tried this:
From the edmx diagram (EF 6), I clicked the column I wanted to hide from EF and on their properties you can set their getter and setter to private. That way, for me it works.
I return some data which includes a User reference, so I wanted to hide the Password field even though it's encrypted and salted, I just didn't want it on my json, and I didn't want to do a:
Select(col => new {})
because that's a pain to create and maintain, especially for big tables with a lot of relationships.
The downside with this method is that if you ever regenerate your model, you would need to modify their getter and setter again.
Using Entity Framework Power Tools you can do the following in efpt.config.json:
"Tables": [
{
"ExcludedColumns": [
"FileData"
],
"Name": "[dbo].[Attachment]",
"ObjectType": 0
}
]
Is there a "best practice" way of handling bulk inserts (via LINQ) but discard records that may already be in the table? Or I am going to have to either do a bulk insert into an import table then delete duplicates, or insert one record at a time?
08/26/2010 - EDIT #1:
I am looking at the Intersect and Except methods right now. I am gathering up data from separate sources, converting into a List, want to "compare" to the target DB then INSERT just the NEW records.
List<DTO.GatherACH> allACHes = new List<DTO.GatherACH>();
State.IState myState = null;
State.Factory factory = State.Factory.Instance;
foreach (DTO.Rule rule in Helpers.Config.Rules)
{
myState = factory.CreateState(rule.StateName);
List<DTO.GatherACH> stateACHes = myState.GatherACH();
allACHes.AddRange(stateACHes);
}
List<Model.ACH> newRecords = new List<Model.ACH>(); // Create a disconnected "record set"...
foreach (DTO.GatherACH record in allACHes)
{
var storeInfo = dbZach.StoreInfoes.Where(a => a.StoreCode == record.StoreCode && (a.TypeID == 2 || a.TypeID == 4)).FirstOrDefault();
Model.ACH insertACH = new Model.ACH
{
StoreInfoID = storeInfo.ID,
SourceDatabaseID = (byte)sourceDB.ID,
LoanID = (long)record.LoanID,
PaymentID = (long)record.PaymentID,
LastName = record.LastName,
FirstName = record.FirstName,
MICR = record.MICR,
Amount = (decimal)record.Amount,
CheckDate = record.CheckDate
};
newRecords.Add(insertACH);
}
The above code builds the newRecords list. Now, I am trying to get the records from this List that are not in the DB by comparing on the 3 field Unique Index:
AchExceptComparer myComparer = new AchExceptComparer();
var validRecords = dbZach.ACHes.Intersect(newRecords, myComparer).ToList();
The comparer looks like:
class AchExceptComparer : IEqualityComparer<Model.ACH>
{
public bool Equals(Model.ACH x, Model.ACH y)
{
return (x.LoanID == y.LoanID && x.PaymentID == y.PaymentID && x.SourceDatabaseID == y.SourceDatabaseID);
}
public int GetHashCode(Model.ACH obj)
{
return base.GetHashCode();
}
}
However, I am getting this error:
LINQ to Entities does not recognize the method 'System.Linq.IQueryable1[MisterMoney.LARS.ZACH.Model.ACH] Intersect[ACH](System.Linq.IQueryable1[MisterMoney.LARS.ZACH.Model.ACH], System.Collections.Generic.IEnumerable1[MisterMoney.LARS.ZACH.Model.ACH], System.Collections.Generic.IEqualityComparer1[MisterMoney.LARS.ZACH.Model.ACH])' method, and this method cannot be translated into a store expression.
Any ideas? And yes, this is completely inline with the original question. :)
You can't do bulk inserts with LINQ to SQL (I presume you were referring to LINQ to SQL when you said "LINQ"). However, based on what you're describing, I'd recommend checking out the new MERGE operator of SQL Server 2008.
Inserting, Updating, and Deleting Data by Using MERGE
Another example here.
I recommend you just write the SQL yourself to do the inserting, I find it is a lot faster and you can get it to work exactly how you want it to. When I did something similar to this (just a one-off program) I just used a Dictionary to hold the ID's I had inserted already, to avoid duplicates.
I find LINQ to SQL is good for one record or a small set that does its entire lifespan in the LINQ to SQL.
Or you can try to use SQL Server 2008's Bulk Insert .
One thing to watch out for is if you queue more than 2000 or so records without calling SubmitChanges() - TSQL has a limit on the number of statements per execution, so you cannot simply queue up every record and then call SubmitChanges() as this will throw an SqlException, you need to periodically clear the queue to avoid this.
Model #1 - This model sits in a database on our Dev Server.
Model #1 http://content.screencast.com/users/Keith.Barrows/folders/Jing/media/bdb2b000-6e60-4af0-a7a1-2bb6b05d8bc1/Model1.png
Model #2 - This model sits in a database on our Prod Server and is updated each day by automatic feeds. alt text http://content.screencast.com/users/Keith.Barrows/folders/Jing/media/4260259f-bce6-43d5-9d2a-017bd9a980d4/Model2.png
I have written what should be some simple code to sync my feed (Model #2) into my working DB (Model #1). Please note this is prototype code and the models may not be as pretty as they should. Also, the entry into Model #1 for the feed link data (mainly ClientID) is a manual process at this point which is why I am writing this simple sync method.
private void SyncFeeds()
{
var sourceList = from a in _dbFeed.Auto where a.Active == true select a;
foreach (RivWorks.Model.NegotiationAutos.Auto source in sourceList)
{
var targetList = from a in _dbRiv.Product where a.alternateProductID == source.AutoID select a;
if (targetList.Count() > 0)
{
// UPDATE...
try
{
var product = targetList.First();
product.alternateProductID = source.AutoID;
product.isFromFeed = true;
product.isDeleted = false;
product.SKU = source.StockNumber;
_dbRiv.SaveChanges();
}
catch (Exception ex)
{
string m = ex.Message;
}
}
else
{
// INSERT...
try
{
long clientID = source.Client.ClientID;
var companyDetail = (from a in _dbRiv.AutoNegotiationDetails where a.ClientID == clientID select a).First();
var company = companyDetail.Company;
switch (companyDetail.FeedSourceTable.ToUpper())
{
case "AUTO":
var product = new RivWorks.Model.Negotiation.Product();
product.alternateProductID = source.AutoID;
product.isFromFeed = true;
product.isDeleted = false;
product.SKU = source.StockNumber;
company.Product.Add(product);
break;
}
_dbRiv.SaveChanges();
}
catch (Exception ex)
{
string m = ex.Message;
}
}
}
}
Now for the questions:
In Model #2, the class structure for Auto is missing ClientID (see red circled area). Now, everything I have learned, EF creates a child class of Client and I should be able to find the ClientID in the child class. Yet, when I run my code, source.Client is a NULL object. Am I expecting something that EF does not do? Is there a way to populate the child class correctly?
Why does EF hide the child entity ID (ClientID in this case) in the parent table? Is there any way to expose it?
What else sticks out like the proverbial sore thumb?
TIA
1) The reason you are seeing a null for source.Client is because related objects are not loaded until you request them, or they are otherwise loaded into the object context. The following will load them explicitly:
if (!source.ClientReference.IsLoaded)
{
source.ClientReference.Load();
}
However, this is sub-optimal when you have a list of more than one record, as it sends one database query per Load() call. A better alternative is to the Include() method in your initial query, to instruct the ORM to load the related entities you are interested in, so:
var sourceList = from a in _dbFeed.Auto .Include("Client") where a.Active == true select a;
An alternative third method is to use something call relationship fix-up, where if, in your example for instance, the related clients had been queried previously, they would still be in your object context. For example:
var clients = (from a in _dbFeed.Client select a).ToList();
The EF will then 'fix-up' the relationships so source.Client would not be null. Obviously this is only something you would do if you required a list of all clients for synching, so is not relevant for your specific example.
Always remember that objects are never loaded into the EF unless you request them!
2) The first version of the EF deliberately does not map foreign key fields to observable fields or properties. This is a good rundown on the matter. In EF4.0, I understand foreign keys will be exposed due to popular demand.
3) One issue you may run into is the number of database queries requesting Products or AutoNegotiationContacts may generate. As an alternative, consider loading them in bulk or with a join on your initial query.
It's also seen as good practice to use an object context for one 'operation', then dispose of it, rather than persisting them across requests. There is very little overhead in initialising one, so one object context per SychFeeds() is more appropriate. ObjectContext implements IDisposable, so you can instantiate it in a using block and wrap the method's contents in that, to ensure everything is cleaned up correctly once your changes are submitted.