I wonder if there is an easy way using Linq to SQL with Entity Framework Core to query check if a given list of ids exist in the database and which returns the list of ids that do not exist.
The use case I come across this is if the user can do something with a list of object (represented through the list of their ids) I want to check if these ids exist or not.
Of course I could query all objects/object ids that exist in the database and cross check in a second step.
Just wondering if it would be possible in one step.
What I mean in code:
public class MyDbObject
{
public int Id { get; set; }
public string Name { get; set; }
}
public IActionResult DoSomethingWithObjects([FromQuery]List<int> ids}
{
List<int> idsThatDoNotExistInTheDb = DbContext.MyDbObject.Where(???)
return NotFound("those ids do not exist: " + string.Join(", ", idsThatDoNotExist));
}
You can obtain the list of IDs that match, then remove them from the original list, like this:
var validIds = DbContext
.MyDbObject
.Where(obj => ids.Contains(obj.Id))
.Select(obj => obj.Id);
var idsThatDoNotExistInTheDb = ids.Except(validIds);
This approach may be slow, though, so you may be better off doing it in a stored procedure that takes a table-valued parameter (how?)
Note: Pre-checks of this kind are not bullet-proof, because a change may happen between the moment when you validate IDs and the moment when you start the operation. It is better to structure your APIs in a way that it validates and then does whatever it needs to do right away. If validation fails, the API returns a list of errors.
I am new to EF. I created entity models from database.
I have tables CurrencyMaster([FromCurrency],[ToCurrency],[ActiveStatus]) and CurrencyConversion([ID],[FromCurrency],[ToCurrency],[Date],[CurrencyFactor])
I am looping for the CurrencyMaster records and accordingly DownloadCurrencyRates will get me the List<CurrencyRate> objects.
I just want to add these objects to entity database.
I tried something like this
public DownloadStatus DownloadUpdateCurrency(DateTime toDate, DateTime fromDate)
{
CurrencyEntities db = new CurrencyEntities();
var curMasters = db.CurrencyMasters.Where(x => x.ActiveStatus == 0);
foreach (var item in curMasters)
{
var curcRatesList = DownloadCurrencyRates(fromDate, toDate,
item.FromCurrency, item.ToCurrency);
//I know this is a bad code
curcRatesList.Select(x =>
{
db.AddToCurrencyConversions(
new CurrencyEntity.CurrencyConversion {
Date = x.date,
CurrencyFactor = x.value,
FromCurrency = item.FromCurrency,
ToCurrency = item.ToCurrency
}
);
return true;
});
}
db.SaveChanges();
return DownloadStatus.DownloadSuccess;
}
How can I do the same in a proper way?
Is there any way I can do this without looping for curcRatesList?
I am using .NET 3.5, and not sure about EF version.. I didn't try executing code(I need some other setup for that), but I am quite sure that what I am doing is not correct.. So I am posting here..
The procedure is correct. There is no bulk insert capability in EF that would allow to add a whole list of entities in a single method call. You must loop over the items and add them one by one.
As a side note: I would just use an ordinary foreach loop instead of that strange Select trick (which misuses the Select method, but it will work). Or - if curcRatesList is of type List<T> - you can use the Foreach method of List<T> instead of Select.
Hi i am trying to get to grips with Dapper.
My situation is i want to pull two values from a query into two separate strings. Im not sure if i am going about this in the correct way, but this is what i am doing:
string sql = #"Select type, name
FROM ZipData
WHERE Zip = #zip";
using (var multi = conn.QueryMultiple(sql, new { zip = zip }))
{
string result = multi.Read<string>().SingleOrDefault();
}
And i am getting Cannot access a disposed object. Object name: 'GridReader'. when trying to read the second string.The thing is it gets the first value correctly and has both the fields in in the reader i am trying to get. Im sure im misusing the api.
What am i doing wrong here? Ive googled but can find a specific example.
You are mis-using QueryMultiple. That is defined for compound SQL statements that return multiple result sets. Something like:
SELECT Foo FROM MyTable;
SELECT Bar FROM MyOtherTable;
On the other hand, you are trying to get two different columns from a single result set, so you should just use the normal Query method:
var result = conn.Query(sql, new { zip = zip }).Single();
var type = result.type;
var name = result.name;
Query returns an enumerable (because generally a query can return multiple rows). It appears that you only want one row, however, so we invoke .Single at the end to just get that row. From there, the return type is dynamic so you can simply refer to the properies implied by the columns in your SELECT statement: type and name.
I'm looking at a problem where I wish to get a collection from an expensive service call and then store it in cache so it can be used for subsequent operations on the UI. The code I'm using is as follows:
List<OrganisationVO> organisations = (List<OrganisationVO>)MemoryCache.Default["OrganisationVOs"];
List<Organisation> orgs = new List<Organisation>();
if (organisations == null)
{
organisations = new List<OrganisationVO>();
orgs = pmService.GetOrganisationsByName("", 0, 4000, ref totalCount);
foreach (Organisation org in orgs)
{
OrganisationVO orgVO = new OrganisationVO();
orgVO = Mapper.ToViewObject(org);
organisations.Add(orgVO);
}
MemoryCache.Default.AddOrGetExisting("OrganisationVOs", organisations, DateTime.Now.AddMinutes(10));
}
List<OrganisationVO> data = new List<OrganisationVO>();
data = organisations;
if (!string.IsNullOrEmpty(filter) && filter != "*")
{
data.RemoveAll(filterOrg => !filterOrg.DisplayName.ToLower().StartsWith(filter.ToLower()));
}
The issue I'm facing is that the data.RemoveAll operation affects the cached version. i.e. I want the cached version to always reflect the full dataset returned by the service call. I then want to retrieve this collection from cache whenever the filter is set and apply it but this should not change cached data - i.e. subsequent filters should happen on the full dataset - what is the best way to do this?
You need to make copy of the list if you want to use RemoveAll operation (ToList would be enough).
Also instead of modigying the list consider using LINQ operations like Where/Select.
I would either:
apply the filter dynamically and replace the filter if needed (so you cache the complete data but only return the cachedData.Where(currentFilter)
make two caches - one for the complete data and one for the filtered data - in this case the first one should only consist of the data returned from the service - no need to cache the VO-data as well
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
}
]