I have the following Entity Framework lambda query:
public IList<MyClass> GetMyClass(int id, bool show)
{
using (var ctx = new DbContext())
{
return ctx.MyClasses.Where(x =>
x.Id == id &&
x.Show == show // <-- nullable bool
.OrderByDescending(x => x.CreationDate).Take(100).ToList();
}
}
My front end view has passed the show boolean down indicating the users preference for what to return.
In the database, the show property is nullable.
This is a very heavy query, so I have limited it to 100 at a time, thousands of rows are null, thousands are true and thousands are false.
Question
How can I say, without making the query inefficient, psuedo code:
.Where(x => x.Show == show) (where null or false == false)
As it stands, if I pass False down, the nulls are excluded, and I need them to be classed as False.
I cannot change the database
how about
(x.Show ?? false) == show
The following code should return records with Show == True when show == true, and records with Show == False or NULL when show == false
private void Repeat(object state)
{
public IList<MyClass> GetMyClass(int id, bool show)
{
using (var ctx = new DbContext())
{
return ctx.MyClasses.Where(x =>
x.Id == id &&
(x.Show == show || !show && x.Show == null)
.OrderByDescending(x => x.CreationDate).Take(100).ToList();
}
}
}
Just another way to think about the expression. Not a good practice in LINQ to Entity.
(x.Show == true) == show
Related
In summary, I'm guessing I can't add any more complex calculations to the LINQ expression. Any tips are greatly appreciated!
This blazor project is using a messy employee table which contains two types of employees, both on the same table
Domestic employees, uses NRG number to identify them, but their NRG numbers are stored as string at NRG column, like "0356".
Foreign employees, also uses NRG to identify them, but their NRG column contains all NULL, their NRG numbers are inside their emails at AzureEmail column, like "johndoe.0356#aaa-bbb.com"
When domestic employee or foreign employee enter their sales records, they are the "Closer", it is required to enter the "Setter" NRG.
By using the "Setter" NRG number "closer" entered, I want to locate the "Setter" info from the same employee table:
public async Task Save_to_SalesForm()
{
await using var context3 = await DBContextFactory.CreateDbContextAsync();
{
if (salesForm.SetterNrg != null && salesForm.CsTransferCategory == "Local Team")
{
setterEmployee = context3.Employees.Where(
e => e.AzureAccountEnabled == 1
&&
(int?)(object?)e.Nrg == salesForm.SetterNrg
).OrderByDescending(e => e.EmployeeId).FirstOrDefault();
salesForm.SetterAgentFullName = setterEmployee.AzureFullName;
salesForm.SetterJobTitle = setterEmployee.AzureRole;
salesForm.SetterEmail = setterEmployee.AzureEmail;
salesForm.SetterTeam = setterEmployee.AzureTeam;
}
if (salesForm.SetterNrg != null && salesForm.CsTransferCategory == "CSR Team (Philippines)")
{
setterEmployee = context3.Employees.Where(
e => e.Nrg == null
&&
e.AzureAccountEnabled == 1
&&
e.AzureEmail.Contains("#aaa-bbb.com")
&&
(int?)(object?)e.AzureEmail.Split(new char[] { '.', '#' }, StringSplitOptions.RemoveEmptyEntries)[1] == salesForm.SetterNrg
).OrderByDescending(e => e.EmployeeId).FirstOrDefault();
salesForm.SetterAgentFullName = setterEmployee.AzureFullName;
salesForm.SetterJobTitle = setterEmployee.AzureRole;
salesForm.SetterEmail = setterEmployee.AzureEmail;
salesForm.SetterTeam = setterEmployee.AzureTeam;
}
}
context3.SalesForms.Add(salesForm);
await context3.SaveChangesAsync();
}
If the "Setter" is a domestic employee (Local Team), the above query works fine and be able to save the setter info to the table
If the "Setter" is a foreign employee (CSR Team (Philippines)), the above query won't work due to the .Split make the query too complex for LINQ expression. Error screenshot
I tried multiple ways to resolve the issue, but none seemed ideal.
I have rewritten your query to use EndsWith, which is translatable to the SQL:
public async Task Save_to_SalesForm()
{
await using var context3 = await DBContextFactory.CreateDbContextAsync();
if (salesForm.SetterNrg != null)
{
Employee? setterEmployee = null;
if (salesForm.CsTransferCategory == "Local Team")
{
setterEmployee = await context3.Employees
.Where(e => e.AzureAccountEnabled == 1
&& (int?)(object?)e.Nrg == salesForm.SetterNrg)
.OrderByDescending(e => e.EmployeeId)
.FirstOrDefaultAsync();
}
else if (salesForm.CsTransferCategory == "CSR Team (Philippines)")
{
var toCheck = $".{salesForm.SetterNrg}#aaa-bbb.com";
setterEmployee = await context3.Employees
.Where(e => e.Nrg == null && e.AzureAccountEnabled == 1
&& e.AzureEmail.EndsWith(toCheck))
.OrderByDescending(e => e.EmployeeId)
.FirstOrDefaultAsync();
}
if (setterEmployee != null)
{
salesForm.SetterAgentFullName = setterEmployee.AzureFullName;
salesForm.SetterJobTitle = setterEmployee.AzureRole;
salesForm.SetterEmail = setterEmployee.AzureEmail;
salesForm.SetterTeam = setterEmployee.AzureTeam;
}
}
context3.SalesForms.Add(salesForm);
await context3.SaveChangesAsync();
}
The problem is in e.AzureEmail.Contains("#aaa-bbb.com"), there is no equivalent in sql to this. Try EF.Functions.Like(e.AzureEmail, "%#aaa-bbb.com%"). Everything from your expression will work if you materialize your data with .ToList() or something and perform it on the client, but it is extremely inefficient.
I have a LINQ query with a WHERE clause that has a variable that sometimes will be NULL. When this variable is NULL I can not get it to pull any results even though there are results to be taken. I found Linq where column == (null reference) not the same as column == null and tried the solutions provided there with no success. What am I doing wrong?
public async Task<List<SectionNavigationMenuDTO>> GetSectionNavigationMenu(int? SectionID, bool IsAdmin = false)
{
return await _siteDbContext.SectionNavigationMenuItems
//.Where(snmi => snmi.SectionID == SectionID && snmi.IsAdminOnly == IsAdmin) //No results at all
//.Where(snmi => object.Equals(snmi.SectionID, SectionID)) //No results at all
//.Where(snmi => (snmi.SectionID == SectionID || (SectionID == null && snmi.SectionID == null))) //No results at all
//.Where(snmi => snmi.IsAdminOnly == IsAdmin) //Returns 3 results
.OrderBy(snmi => snmi.Name)
.Select(sni => new SectionNavigationMenuDTO()
{
Name = sni.Name,
URL = sni.URL
})
.ToListAsync();
}
Edit:
The SectionID should be either filled with a int or null and be valid in both cases. If the SectionID variable is NULL then it should pass NULL as the argument in for the LINQ query. The database does contain entries with NULL for the SectionID and the query SELECT * FROM dbo.SectionNavigationMenuItems WHERE SectionID IS NULL does return 3 results as expected.
The top commented WHERE clause is what I want to happen (with the two comparisons) the other 3 are what I have tried to get this to work and the results.
Try this:
public async Task<List<SectionNavigationMenuDTO>> GetSectionNavigationMenu(int? SectionID, bool IsAdmin = false)
{
return await _siteDbContext.SectionNavigationMenuItems
.Where(snmi => snmi.IsAdminOnly == IsAdmin && (SectionID==null || SectionID==smi.SectionID ) )
.OrderBy(snmi => snmi.Name)
.Select(sni => new SectionNavigationMenuDTO()
{
Name = sni.Name,
URL = sni.URL
})
.ToListAsync();
}
I'm working on small app for fetching products/articles, and I wrote a method that's getting articles by type. (types are contained in request arg).
What I'm trying to achieve is: append all results (from all if conditions if they are satisfied) to one main list which should be returned to customer..
When I'm debugging and checking query it says its returning type is IQueryable<Article> so basically my question is how can I append multiple IQueryables into one which should be returned to user..
This code below is not working because result is always empty..
I've tried also with var result = new List<Article>(); and later result.AddRange(query); and I've changed also return type to
return await result.AsQueryable().ToListAsync(); but obviously something breaks somewhere and I get an empty array at the end.
public async Task<IEnumerable<Article>> GetArticlesByType(ArticleObject request)
{
var result = new Article[] { }.AsQueryable();
IQueryable<ArticleDTO> query = null;
if (request.Food.HasValue && (bool)request.Food)
{
// Return type of query is IQueryable<Article>
query = _context.Articles.Where(x => x.Active == true && x.ArticleType == ArticleType.Food).Select(x => new Article
{
Id = x.Id,
ArticleName = x.ArticleName
});
// Here I just wanted if this condition is satisfied to add values to my result
result.AsQueryable().Union(query);
}
if (request.Drink.HasValue && (bool)request.Drink)
{
query = _context.Articles.Where(x => x.Active == true && x.ArticleType == ArticleType.Drink).Select(x => new Article
{
Id = x.Id,
ArticleName = x.ArticleName
});
// Again if there are any values in query add them to existing result values
result.AsQueryable().Union(query);
}
if (request.Candy.HasValue && (bool)request.Candy)
{
// When its candy I want also articles from food category
query = _context.Articles.Where(x => x.Active == true && x.ArticleType == ArticleType.Food || x.ArticleType == ArticleType.Candy).Select(x => new Article
{
Id = x.Id,
ArticleName = x.ArticleName
});
// Again if there are values in query add them to existing result
result.AsQueryable().Union(query);
}
//At the end return result and all the values in case all conditions were satisfied
return await result.ToListAsync();
}
Try with result.AsQueryable().Union(query.ToList());. This will fetch the object from database. So far query contains references to objects in database and not in your memory
I was originally using a foreach loop and then for each element in the loop, I perform a LINQ query like so:
foreach (MyObject identifier in identifiers.Where(i => i.IsMarkedForDeletion == false))
{
if (this.MyEntities.Identifiers.Where(pi => identifier.Field1 == pi.Field1 && identifier.Field2 == pi.Field2 && identifier.Field3 == pi.Field3).Any())
{
return false;
}
}
return true;
Then I modified it like so:
if (identifiers.Any(i => !i.IsMarkedForDeletion && this.MyEntities.Identifiers.Where(pi => i.Field1 == pi.Field1 && i.Field2 == pi.Field2 && i.Field3 == pi.Field3).Any()))
{
return false;
}
return true;
My question is this still the wrong way to use LINQ? Basically, I want to eliminate the need for the foreach loop (which seems like I should be able to get rid of it) and also make the DB query faster by not performing separate DB queries for each element of a list. Instead, I want to perform one query for all elements. Thanks!
You can change your code in this way, and it will be converted to SQL statement as expected.
To prevent runtime errors during transformation, it will be better to save DBSet to the IQueryable variable; identifiers should be IQueryable too, so you should change your code into something like this (to be honest, Resharper converted your foreach in this short labda):
IQueryable<MyObject2> identifiers = MyEntities.Identifiers.Where(i => i.IsMarkedForDeletion == false);
IQueryable<MyObject2> ids = MyEntities.Identifiers.AsQueryable();
return identifiers.All(identifier => !ids.Any(pi => identifier.Field1 == pi.Field1 && identifier.Field2 == pi.Field2 && identifier.Field3 == pi.Field3));
If identifiers is in memory collection you can change code in this way (hope that fields are string):
IQueryable<MyObject2> ids = MyEntities.Identifiers.AsQueryable();
string[] values = identifiers.Where(i => i.IsMarkedForDeletion == false).Select(i => String.Concat(i.Field1, i.Field2, i.Field3)).ToArray();
return !ids.Any(i => values.Contains(i.Field1 + i.Field2 + i.Field3));
Unfortunately your modified version will be executed exactly the same way (i.e. multiple database queries) as in the original foreach approach because EF does not support database query with joins to in memory collection (except for primitive and enumeration type collections), so if you try the most logical way
bool result = this.MyEntities.Identifiers.Any(pi => identifiers.Any(i =>
!i.IsMarkedForDeletion &&
i.Field1 == pi.Field1 && i.Field2 == pi.Field2 && i.Field3 == pi.Field3));
you'll get
NotSupportedException: Unable to create a constant value of type 'YourType'. Only primitive types or enumeration types are supported in this context.
The only way to let EF execute a single database query is to manually build a LINQ query with Concat per each item from in memory collection, like this
IQueryable<Identifier> query = null;
foreach (var item in identifiers.Where(i => !i.IsMarkedForDeletion))
{
var i = item;
var subquery = this.MyEntities.Identifiers.Where(pi =>
pi.Field1 == i.Field1 && pi.Field2 == i.Field2 && pi.Field3 == i.Field3);
query = query != null ? query.Concat(subquery) : subquery;
}
bool result = query != null && query.Any();
See Logging and Intercepting Database Operations of how to monitor the EF actions.
I would use it as follows:
if (identifiers.Where(i => !i.IsMarkedForDeletion &&
this.MyEntities.Identifiers.Field1 == i.Field1 &&
this.MyEntities.Identifiers.Field2 == i.Field2 &&
this.MyEntities.Identifiers.Field3 == i.Field3).Any()))
{
return false;
}
return true;
I hope this helps. Even though it is more to type out, it is more understandable and readable then using multiple 'where' statements.
I have the following code:
IsServiceable = _context.Review.Any(r => r.SiteId == x.Id) ? _context.Review.All(r => r.SiteId == x.Id && r.IsValid == true) : true
But as you can see it is not effective because I try to access the database twice in the same row.
I need to write single query(LINQ TO ENTITY) to check if the table named Reviews
has at least one row
where siteId=5 if it doesn't it has to return true,
If table Reviews has at least one row I need to check a boolean column named isValid if, there is at least one row where siteId=5 and isValid column is false I need to return false.
I believe your solution lies in the fact that only in one case do you need to return false - everything else returns true. Therefore, if you find one row where sideId=5 and isValid = false, then return false. Otherwise, return true. Based on your code, I suggest something like the following:
IsServiceable = _context.InspectionReview.Any(r => r.SiteId == x.Id && r.isValid == false) ? false : true;
You most likely have navigation properties so you could try
IsServiceable = _context.Site.Any(s => s.Id == x.Id && s.Reviews.Any(r => r.IsValid));