Here’s some pretty basic reasons. (1) If a query (insert, update, delete) violates a constraint, SQL will generate an error message that will contain the constraint name. If the constraint name is clear and descriptive, the error message will be easier to understand; if the constraint name is a random guid-based name, it’s a lot … Read more
You should use the current sys catalog views (if you’re on SQL Server 2005 or newer – the sysobjects views are deprecated and should be avoided) – check out the extensive MSDN SQL Server Books Online documentation on catalog views here. There are quite a few views you might be interested in: sys.default_constraints for default … Read more
The relationship between UIScrollView and auto layout is different from other aspects of auto layout. Basically, if simple auto layout were allowed to operate, nothing would scroll. For example, if a subview of the scroll view were pinned in the normal way by a constraint to 10 points from the top of the scroll view, … Read more
A number of classes are unavailable as generic contraints – Enum being another. For delegates, the closest you can get is “: class”, perhaps using reflection to check (for example, in the static constructor) that the T is a delegate: static GenericCollection() { if (!typeof(T).IsSubclassOf(typeof(Delegate))) { throw new InvalidOperationException(typeof(T).Name + ” is not a delegate … Read more
If you use C++11, you can use static_assert with std::is_base_of for this purpose. For example, #include <type_traits> template<typename T> class YourClass { YourClass() { // Compile-time check static_assert(std::is_base_of<BaseClass, T>::value, “type parameter of this class must derive from BaseClass”); // … } }
When using Auto Layout in code, setting the frame does nothing. So the fact that you specified a width of 200 on the view above, doesn’t mean anything when you set constraints on it. In order for a view’s constraint set to be unambiguous, it needs four things: an x-position, a y-position, a width, and … Read more
You can group them all in the same alter statement: alter table tbl alter col1 drop not null, alter col2 drop not null, … You can also retrieve the list of relevant columns from the catalog, if you feel like writing a do block to generate the needed sql. For instance, something like: select a.attname … Read more
alter table MYTABLE modify (MYCOLUMN null); In Oracle, not null constraints are created automatically when not null is specified for a column. Likewise, they are dropped automatically when the column is changed to allow nulls. Clarifying the revised question: This solution only applies to constraints created for “not null” columns. If you specify “Primary Key” … Read more
As stated in NSLayoutConstraint class reference: Priorities may not change from nonrequired to required, or from required to nonrequired. An exception will be thrown if a priority of NSLayoutPriorityRequired in OS X or UILayoutPriorityRequired in iOS is changed to a lower priority, or if a lower priority is changed to a required priority after the … Read more
Constraints are part of a database schema definition. A constraint is usually associated with a table and is created with a CREATE CONSTRAINT or CREATE ASSERTION SQL statement. They define certain properties that data in a database must comply with. They can apply to a column, a whole table, more than one table or an … Read more