There's a way in LINQ to convert this following sql code ?
public Category SaveCategory(Category category, string tableName)
{
var context = new MyEntities();
context.Database.ExecuteSqlCommand("INSERT INTO " + tableName + " (title,description) VALUES {0}{1} ", table.title, table.description);
}
I want to avoid the use of conditions like "if" and "switch case" like :
case "Country": tableName= db.Countries.FirstOrDefault(x => x.id == id);
break;
case "City": tableName= db.Cities.FirstOrDefault(x => x.id == id);
break;
...
return tableName
If you can use Types instead of strings, you can use the Set method of the DbContext.
Type tableType = // type representing Country
DbSet mySet = db.Set(tableType);
mySet.Add(whatever);
Or you can access the Database property, but your code is potentially open to SQL injection. You should validate the string against a whitelist of valid table names, or do something else to remove the possibility of injection.
db.Database.ExecuteSqlCommand(...);
Related
When building a complex SQL query for Laravel, using ? as placeholders for parameters is great. However when the value is null, the SQL syntax needs to be changed from = ? to IS NULL. Plus, since the number of parameters is one less, I need to pass a different array.
To get it to work, I have written it like this, but there must be a better way:
if ($cohortId === null) {
// sql should be: column IS NULL
$sqlCohortString = "IS NULL";
$params = [
Carbon::today()->subDays(90),
// no cohort id here
];
} else {
// sql should be: column = ?
$sqlCohortString = "= ?";
$params = [
Carbon::today()->subDays(90),
$cohortId
];
}
$query = "SELECT items.`name`,
snapshots.`value`,
snapshots.`taken_at`,
FROM snapshots
INNER JOIN (
SELECT MAX(id) AS id, item_id
FROM snapshots
WHERE `taken_at` > ?
AND snapshots.`cohort_id` $sqlCohortString
GROUP BY item_id
) latest
ON latest.`id` = snapshots.`id`
INNER JOIN items
ON items.`id` = snapshots.`item_id`
ORDER by media_items.`slug` ASC
";
$chartData = DB::select($query, $params);
My question is: does Laravel have a way to detect null values and replace ? more intelligently?
PS: The SQL is for a chart, so I need the single highest snapshot value for each item.
You can use ->when to create a conditional where clause:
$data = DB::table('table')
->when($cohortId === null, function ($query) {
return $query->whereNull('cohort_id');
}, function ($query) use ($cohortId) {
// the "use" keyword provides access to "outer" variables
return $query->where('cohort_id', '=', $cohortId);
})
->where('taken_at', '>', $someDate)
->toSql();
I'm working with a legacy Oracle database that has a column on a table which stores boolean values as 'Y' or 'N' characters.
I have mapped/converted this column out like so:
MappingSchema.Default.SetConverter<char, bool>(ConvertToBoolean);
MappingSchema.Default.SetConverter<bool, char>(ConvertToChar);
ConvertToBoolean & ConvertToChar are simply functions that map between the types.
Here's the field:
private char hasDog;
[Column("HAS_DOG")]
public bool HasDog
{
get => ConvertToBoolean(hasDog);
set => hasDog = ConvertToChar(value);
}
This has worked well for simply retrieving data, however, it seems the translation of the following:
var humanQuery = (from human in database.Humans
join vetVisit in database.VetVisits on human.Identifier equals vetVisit.Identifier
select new HumanModel(
human.Identifier
human.Name,
human.HasDog,
vetVisit.Date,
vetVisit.Year,
vetVisit.PaymentDue
));
// humanQuery is filtered by year here
var query = from vetVisits in database.VetVisits
select new VetPaymentModel(
(humanQuery).First().Year,
(humanQuery).Where(q => q.HasDog).Sum(q => q.PaymentDue), -- These 2 lines aren't correctly translated to Y/N
(humanQuery).Where(q => !q.HasDog).Sum(q => q.PaymentDue)
);
As pointed out above, the .Where clause here doesn't translate the boolean comparison of HasDog being true/false to the relevant Y/N values, but instead a 0/1 and results in the error
ORA-01722: invalid number
Is there any way to handle this case? I'd like the generated SQL to check that HAS_DOG = 'Y' for instance with the specified Where clause :)
Notes
I'm not using EntityFramework here, the application module that this query exists in doesn't use EF/EFCore
You can define new mapping schema for your particular DataConnection:
var ms = new MappingSchema();
builder = ms.GetFluentMappingBuilder();
builder.Entity<Human>()
.Property(e => e.HasDog)
.HasConversion(v => v ? 'Y' : 'N', p => p == 'Y');
Create this schema ONCE and use when creating DataConnection
How can i dynamically change the selected columns in the generated sql query when using a linq expression?
Its a new session for each time the query is executed.
Even when I set the MapExp as null after first creation an then changing the bool value to false, it still generates the column in the sql query.
The code runs in a wpf application.
System.Linq.Expressions.Expression<Func<Entity, Model>> MapExp = x => new Model
{
Id=xId,
Count= LoadFormulaField ? x.Count: null,
...
};
var result = session.Query<Entity>().Select(MapExp))
Your problem seems to be the ternary-conditional as part of the expression which is causing the "Count" column to always be queried.
One option to avoid this could be:
var query = session.Query<Entity>();
IQueryable<Model> result = null;
if (LoadFormulaField)
{
result = query.Select(x => new Model
{
Id = x.Id,
Count = x.Count,
});
}
else
{
result = query.Select(x => new Model
{
Id = x.Id,
});
}
Which would get a little less ugly if you separate in a couple of methods I think.
Really stuck with Linq to SQL grouping and summing, have searched everywhere but I don't understand enough to apply other solutions to my own.
I have a view in my database called view_ProjectTimeSummary, this has the following fields:
string_UserDescription
string_ProjectDescription
datetime_Date
double_Hours
I have a method which accepts a to and from date parameter and first creates this List<>:
List<view_UserTimeSummary> view_UserTimeSummaryToReturn =
(from linqtable_UserTimeSummaryView
in datacontext_UserTimeSummary.GetTable<view_UserTimeSummary>()
where linqtable_UserTimeSummaryView.datetime_Week <= datetime_To
&& linqtable_UserTimeSummaryView.datetime_Week >= datetime_From
select linqtable_UserTimeSummaryView).ToList<view_UserTimeSummary>();
Before returning the List (to be used as a datasource for a datagridview) I filter the string_UserDescription field using a parameter of the same name:
if (string_UserDescription != "")
{
view_UserTimeSummaryToReturn =
(from c in view_UserTimeSummaryToReturn
where c.string_UserDescription == string_UserDescription
select c).ToList<view_UserTimeSummary>();
}
return view_UserTimeSummaryToReturn;
How do I manipulate the resulting List<> to show the sum of the field double_Hours for that user and project between the to and from date parameters (and not separate entries for each date)?
e.g. a List<> with the following fields:
string_UserDescription
string_ProjectDescription
double_SumOfHoursBetweenToAndFromDate
Am I right that this would mean I would have to return a different type of List<> (since it has less fields than the view_UserTimeSummary)?
I have read that to get the sum it's something like 'group / by / into b' but don't understand how this syntax works from looking at other solutions... Can someone please help me?
Thanks
Steve
Start out by defining a class to hold the result:
public class GroupedRow
{
public string UserDescription {get;set;}
public string ProjectDescription {get;set;}
public double SumOfHoursBetweenToAndFromDate {get;set;}
}
Since you've already applied filtering, the only thing left to do is group.
List<GroupedRow> result =
(
from row in source
group row by new { row.UserDescription, row.ProjectDescription } into g
select new GroupedRow()
{
UserDescription = g.Key.UserDescription,
ProjectDescription = g.Key.ProjectDescription,
SumOfHoursBetweenToAndFromDate = g.Sum(x => x.Hours)
}
).ToList();
(or the other syntax)
List<GroupedRow> result = source
.GroupBy(row => new {row.UserDescription, row.ProjectDescription })
.Select(g => new GroupedRow()
{
UserDescription = g.Key.UserDescription,
ProjectDescription = g.Key.ProjectDescription,
SumOfHoursBetweenToAndFromDate = g.Sum(x => x.Hours)
})
.ToList();
I need to filter some Entities by various fields using "normal" WHERE and IN clauses in a query over my database, but I do not know how to do that with EF.
This is the approach:
Database table
Licenses
-------------
license INT
number INT
name VARCHAR
...
desired SQL Query in EF
SELECT * FROM Licenses WHERE license = 1 AND number IN (1,2,3,45,99)
EF Code
using (DatabaseEntities db = new DatabaseEntities ())
{
return db.Licenses.Where(
i => i.license == mylicense
// another filter
).ToList();
}
I have tried with ANY and CONTAINS, but I do not know how to do that with EF.
How to do this query in EF?
int[] ids = new int[]{1,2,3,45,99};
using (DatabaseEntities db = new DatabaseEntities ())
{
return db.Licenses.Where(
i => i.license == mylicense
&& ids.Contains(i.number)
).ToList();
}
should work