set

问题 The error Cannot delete or update a parent row: a foreign key constraint fails. The classes class Teacher { /** *@ORM\OneToMany(targetEntity="publication", mappedBy="teacher") */ protected $publications; } class Publication { /** * @ORM\ManyToOne(targetEntity="Teacher", inversedBy="publications") * @ORM\JoinColumn(name="teacher_id", referencedColumnName="id") */ protected $teacher; } I want What I want is to make it that when you delete a teacher, the id_teacher is modified to NULL. I want to

问题 The error Cannot delete or update a parent row: a foreign key constraint fails. The classes class Teacher { /** *@ORM\OneToMany(targetEntity="publication", mappedBy="teacher") */ protected $publications; } class Publication { /** * @ORM\ManyToOne(targetEntity="Teacher", inversedBy="publications") * @ORM\JoinColumn(name="teacher_id", referencedColumnName="id") */ protected $teacher; } I want What I want is to make it that when you delete a teacher, the id_teacher is modified to NULL. I want to

问题 I'm elaborating on this question (Copy Column Value from One table into Another Matching IDs - SQLite) by adding an extra challenge. The idea is to copy the value of several columns from one table to another when an id is matching. The aforementioned question addresses how to copy the content of one column when a matching id is found. Here the code as posted by @scaisEdge: UPDATE t1 SET value = ( SELECT value FROM t2 WHERE t1.ID = t2.ID) But what if we want to update several columns from that

问题 I'm elaborating on this question (Copy Column Value from One table into Another Matching IDs - SQLite) by adding an extra challenge. The idea is to copy the value of several columns from one table to another when an id is matching. The aforementioned question addresses how to copy the content of one column when a matching id is found. Here the code as posted by @scaisEdge: UPDATE t1 SET value = ( SELECT value FROM t2 WHERE t1.ID = t2.ID) But what if we want to update several columns from that

问题 I have two large lists train and keep , with the latter containing unique elements, for e.g. train = [1, 2, 3, 4, 5, 5, 5, 5, 3, 2, 1] keep = [1, 3, 4] Is there a way to create a new list that has all the elements of train that are in keep using sets ? The end result should be: train_keep = [1, 3, 4, 3, 1] Currently I'm using itertools.filterfalse from how to keep elements of a list based on another list but it is very slow as the lists are large... 回答1: Convert the list keep into a set ,

问题 I have two large lists train and keep , with the latter containing unique elements, for e.g. train = [1, 2, 3, 4, 5, 5, 5, 5, 3, 2, 1] keep = [1, 3, 4] Is there a way to create a new list that has all the elements of train that are in keep using sets ? The end result should be: train_keep = [1, 3, 4, 3, 1] Currently I'm using itertools.filterfalse from how to keep elements of a list based on another list but it is very slow as the lists are large... 回答1: Convert the list keep into a set ,

问题 I have a MySQL query that gives the error: "Error Code: 1104. The SELECT would examine more than MAX_JOIN_SIZE rows; check your WHERE and use SET SQL_BIG_SELECTS=1 or SET MAX_JOIN_SIZE=# if the SELECT is okay" To run this successfully in MySQL Workbench, I simply execute: SET SESSION SQL_BIG_SELECTS = 1; SELECT ... FROM ... WHERE ...; This runs both statements at once - SQL_BIG_SELECTS is set to 1 which allows the query below it to run. Now I want to access the result of this query in python

问题 Does anyone know how to stop >nul being ignored when set in a variable, or is this not possible? I have a feeling that it's one of those things that will only work once all variables have been expanded or something, but it can't hurt to ask. Example: @echo off :: Won't work SET pause_5=ping localhost /n 6 >nul %pause_5% :: Will work SET pause_5=ping localhost /n 6 %pause_5% >nul exit 回答1: Put quotes around the argument: set "pause_5=ping localhost /n 6 >nul" Another option is to escape

问题 I am trying to solve a problem in computational algebra using python. Basically given two sets, say A={a,b} and B={e} , I need to compute the element by element tensor products and get a final set say C={a\tensor{e},b\tensor{e}} containing these products of elements. I can do an element by element multiplication using arrays with numbers but I can't do an element by element tensor multiplication of letters instead of numbers. 回答1: Not sure if I understood correctly, this below code multiplies

问题 According to the Ruby Set class's documentation, "== Returns true if two sets are equal. The equality of each couple of elements is defined according to Object#eql?. The essence of this can be demonstrated using Date objects, where sets containing different Date objects but with the same date compare to equal: require 'set' d1 = Date.today # => Thu, 30 Sep 2010 puts d1.object_id # => 2211539680 d2 = Date.today + 1 # => Fri, 01 Oct 2010 puts d2.object_id # => 2211522320 set1 = Set.new([d1, d2]