constraints

问题 I am busy adding database (SQLite) support to my latest application. Since there are some tables that has rows that reference rows in other tables I thought it might be a good idea to start using foreign key constraints. A few google searches later I was able to apply the constraints to one table as a test run. var c = workingDataSet.Tables["measurements"].Columns["reference_realestate"]; var p = workingDataSet.Tables["realestates"].Columns["id"]; ForeignKeyConstraint fkcon = new

问题 I have two blocks of code, one working and the second not really. The first adds a view, constraints its height to 0 and then cancel this constraint in an animation block so it grows up. Works perfect. The second one is supposed to reactivate the 0 height constraint so that its height shrinks back to 0 and then remove it, but instead it is removed instantaneously. Here's the code: self.pickupAddressViewModel.infoViewBlock = ^(MandatoryPickupView * _Nonnull pickupView) { if (weakSelf

问题 I'm biting the bullet and have begun using auto layout. Not as difficult to get used to than I feared. I am having trouble with this though. Is it possible for view 2 to 'anchor' to the bottom of view 1.. UNLESS view 1 is hidden, in which case it should anchor to the top of the containing view? How would I set constraints for this? If View1.hidden = NO: If View1.hidden = YES: 回答1: Perhaps the easiest way to solve this issue is to manipulate constraint priorities. I won't go into detail

问题 I'm new to Oracle SQL and I am having a hard time adding a constraint. I am trying to add constraints on my table to enforce specific business rules that only allows students only to take 4 courses and a max of 25 students per class. Please let me know what additional information you need from me to help answer this question. I am at a loss... CREATE TABLE GRADES (STU_ID int NOT NULL ENABLE, CRSE_ID CHAR(9) NOT NULL ENABLE, STU_CRSE_GRADE VARCHAR2(20) check(STU_CRSE_GRADE='A' or STU_CRSE

问题 I'm creating a table in Oracle 11g like this: CREATE TABLE EXAMPLE ( ID VARCHAR2(10) PRIMARY KEY, NAME VARCHAR2(100), SHORT VARCHAR2(50), CURRENCY CHAR(3) ); Is it possible to create a foreign key constraint or even a check constraint on CURRENCY to a built-in Oracle table that contains the ISO currencies? Not having a great understanding of databases I also take as input other solutions that might be out there, however I do not want to maintain my own table for this, if it's too much work, I

问题 I have something like this: CREATE TYPE oAuthors AS OBJECT ( ... , contract CHAR(1), CONSTRUCTOR FUNCTION oAuthors (... ); The thing is that I wanted to add a constraint to allow only 0 or 1 in contract. I tried to do so right after the declaration of the column by adding CONSTRAINT contract_bit CHECK (contract IN ('0','1')), I also tried to do it in an ALTER sentence, but the problem is that this is not a table so it won't recognize it, and using ALTER TYPE doesn't work (although I was just

问题 I have a Rails application setup where, after all of the other site routes are defined, I have a catch-all wildcard for my Users to display their Profiles on selected root-level "vanity" URLs of non-reserved paths/keywords: get '*path' => 'profiles#show' The Profiles controller then checks to make sure the path defines a valid Profile, otherwise redirects to root. This works fine. What I need to do now is create a mechanism where the catch-all path could define either a Profile or a Blog,

问题 I'm trying to write a solver for End View Puzzles, using CLPFD (for those who are unfamiliar, here's a simple description http://www.funwithpuzzles.com/2009/12/abcd-end-view-a1.html ). I'm working on the constraint that I'll apply to each row/column, and running into some trouble. So I'm thinking it should look something like this: % NxN board, numbers from 0 to M in the row, Left/Right are the clues % corresponding to the row endviews(N,M,List,Left,Right):- length(List,M), domain(List,0,M),

问题 My Swing applications throws few exceptions. I tried to catch Integrity Constraint Violation Exception and display message "Duplicate ID". But when that happened, without catching it here: catch(MySQLIntegrityConstraintViolationException ex) it goes to catch (SQLException ex). What I want to do is, catch Integrity Violation exception and display user friendly message instead of technical message comes from ex.getMessage(). How do I do this? ShippmentTransfer shipTrns = new ShippmentTransfer

问题 I have three tables, table A has a unique primary key that is auto-incremented, and the other two (table B and C) have primary keys that have a foreign key constraint that ties them to the first tables primary key. I want to make a constraint that maintains that for all rows in the second and third tables they cannot contain any duplicate, and for all records in table A there is a matching record in B or C. So basically a record of type A can be a type B or C and must be one of B or C. Is