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Unique Key constraints for multiple columns in Entity Framework
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Unique indexes in EntityFramework Core:
First approach:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Entity>()
.HasIndex(p => new {p.FirstColumn , p.SecondColumn}).IsUnique();
}
The second approach to create Unique Constraints with EF ...
Best way to define private methods for a class in Objective-C
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There isn't, as others have already said, such a thing as a private method in Objective-C. However, starting in Objective-C 2.0 (meaning Mac OS X Leopard, iPhone OS 2.0, and later) you can create a category with an empty name (i.e. @interface MyClass ()) called C...
Can I apply a CSS style to an element name?
...the HTML is not very well labelled, in the sense that there are not enough id and class declarations to differentiate between elements.
...
What is the best way to deal with the NSDateFormatter locale “feechur”?
...t "NSDateFormatter+Locale.h"
@implementation NSDateFormatter (Locale)
- (id)initWithSafeLocale {
static NSLocale* en_US_POSIX = nil;
self = [self init];
if (en_US_POSIX == nil) {
en_US_POSIX = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
}
[self setLocale...
SPAN vs DIV (inline-block)
...using the display CSS property but there is one issue: in terms of HTML validation, you can't put block elements inside inline elements so:
<p>...<div>foo</div>...</p>
is not strictly valid even if you change the <div> to inline or inline-block.
So, if your element ...
Injecting $scope into an angular service function()
...ing with the server.
var save = function (student) {
if (student.id === null) {
students.push(student);
} else {
for (var i = 0; i < students.length; i++) {
if (students[i].id === student.id) {
students[i] = student;
break;
...
Is it possible to use the instanceof operator in a switch statement?
...ario where subtype polymorphism helps. Do the following
interface I {
void do();
}
class A implements I { void do() { doA() } ... }
class B implements I { void do() { doB() } ... }
class C implements I { void do() { doC() } ... }
Then you can simply call do() on this.
If you are not free to ...
What is an xs:NCName type and when should it be used?
...NCNames (not qualified names):
namespace prefixes
values representing an ID
values representing an IDREF
values representing a NOTATION
processing instruction targets
entity names
share
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improve...
What's the difference between “Request Payload” vs “Form Data” as seen in Chrome dev tools Network t
I have an old web application I have to support (which I did not write).
2 Answers
2
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How to update column with null value
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No special syntax:
CREATE TABLE your_table (some_id int, your_column varchar(100));
INSERT INTO your_table VALUES (1, 'Hello');
UPDATE your_table
SET your_column = NULL
WHERE some_id = 1;
SELECT * FROM your_table WHERE your_column IS NULL;
+---------+-------------+
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