relation

问题 So I'm trying to find indirect relations in a dictionary but I can't seem to find a general code for my program: this is what I have #find if A is related to E data = {"A": {"B": 5, "C": 7}, "B": {"E": 8}, "C": {}, "D": {}, "E": {"D": 9}} if "E" in data["A"]: result = True if "E" in data["B"] or "D" in data["C"]: result = True else: result = False print(result) #output = True because "E" is in data["A"] For this one example it works and ofcourse I've could generalize this with x's and y's but

问题 So I'm trying to find indirect relations in a dictionary but I can't seem to find a general code for my program: this is what I have #find if A is related to E data = {"A": {"B": 5, "C": 7}, "B": {"E": 8}, "C": {}, "D": {}, "E": {"D": 9}} if "E" in data["A"]: result = True if "E" in data["B"] or "D" in data["C"]: result = True else: result = False print(result) #output = True because "E" is in data["A"] For this one example it works and ofcourse I've could generalize this with x's and y's but

问题 I want to return the sum of "amount" from my payments table. There can be many payments for one invoice. The below "->sum('amount') does not work, it returns: Call to a member function addEagerConstraints() on a non-object. How to return the sum of all payments for each invoice in my relation? Invoices Model: class Invoices extends Eloquent { public function payments() { return $this->hasMany('Payments')->sum('amount'); } } Expenses Model: class Payments extends Eloquent { public function

问题 I want to return the sum of "amount" from my payments table. There can be many payments for one invoice. The below "->sum('amount') does not work, it returns: Call to a member function addEagerConstraints() on a non-object. How to return the sum of all payments for each invoice in my relation? Invoices Model: class Invoices extends Eloquent { public function payments() { return $this->hasMany('Payments')->sum('amount'); } } Expenses Model: class Payments extends Eloquent { public function

问题 I want to return the sum of "amount" from my payments table. There can be many payments for one invoice. The below "->sum('amount') does not work, it returns: Call to a member function addEagerConstraints() on a non-object. How to return the sum of all payments for each invoice in my relation? Invoices Model: class Invoices extends Eloquent { public function payments() { return $this->hasMany('Payments')->sum('amount'); } } Expenses Model: class Payments extends Eloquent { public function

问题 I want to return the sum of "amount" from my payments table. There can be many payments for one invoice. The below "->sum('amount') does not work, it returns: Call to a member function addEagerConstraints() on a non-object. How to return the sum of all payments for each invoice in my relation? Invoices Model: class Invoices extends Eloquent { public function payments() { return $this->hasMany('Payments')->sum('amount'); } } Expenses Model: class Payments extends Eloquent { public function

问题 I want to return the sum of "amount" from my payments table. There can be many payments for one invoice. The below "->sum('amount') does not work, it returns: Call to a member function addEagerConstraints() on a non-object. How to return the sum of all payments for each invoice in my relation? Invoices Model: class Invoices extends Eloquent { public function payments() { return $this->hasMany('Payments')->sum('amount'); } } Expenses Model: class Payments extends Eloquent { public function

问题 When your creating a database schema and come up with all the foreign keys. What are the advantages of explicitly defining them as such in the database? Are there advantages? If it's reliant MySQL is the db I will be using. 回答1: Foreign key constraints are used for maintaining Referential Integrity which is a database constraint that ensures that references between data are indeed valid and intact (a database should not only store data but should also ensure its quality). In other words, they

问题 I am learning jpa through some examples ,involving a shopping cart and cart items.I defined them as below..but am not very sure about which mapping to use @Entity class Product{ private Long id; private String name; ... } @Entity class CartItem{ private Long id; private Product product; private int quantity; ... } @Entity class ShoppingCart{ private Long id; @OneToMany private Set<CartItem> cartItems; ... } What I am not very sure of ,is how to relate between Product and CartItem and how to

问题 I have an Activities model, and they belong_to a Location How do i select all the activities whose location.country = Australia? (for example) Can I do this within a scope? 回答1: The kind of query you're talking about is a join. You can try queries like this in the console like: Activity.joins(:locations).where('locations.country = "Australia"') This means that SQL is going to take all the activities and locations associated with then, find the locations where country=Australia, and then