data-modeling

问题 In a relational DB, I could have a table Person and a table Hobby . Every person can have zero, one or more hobbies , and I also want to record, say, the priority of those hobbies for every person . I could create a relationship table with the 2 foreign keys PersonFK and HobbyFK , and one plain column Priority . In datomic, to model a simple n:m relationship (without the priority), I'd probably create an attribute of type Reference with cardinality Many , that I'd use for Person entities. But

问题 I'm modeling an entity relationship diagram and got stuck. I'm not sure if my considerations are wrong or an ERD can't modell what I want: I have three entities: Employee, Project and Role. There is a relation between Employee and Project: an employee is working on a project. But this employee isn't just working on this project, he/she has a field of operation that is given as a role. But isn't a relation just described by attributes? How can I make something like "An employee works on this

问题 When we initially designed our project, we had a couple of entities that to date are unused (and we don't plan to implement them in the near future). Ergo I want to remove them from my project. I would proceed like this (all steps manually performed): Remove all relations from my currently used entities. Delete the doctrime ORM file src/Resources/config/doctrine Delete the class PHP file from src/Entity Remove the table from the database What I would like to know: Are there any routines (e.g.

问题 When we initially designed our project, we had a couple of entities that to date are unused (and we don't plan to implement them in the near future). Ergo I want to remove them from my project. I would proceed like this (all steps manually performed): Remove all relations from my currently used entities. Delete the doctrime ORM file src/Resources/config/doctrine Delete the class PHP file from src/Entity Remove the table from the database What I would like to know: Are there any routines (e.g.

问题 I have an application where the 'natural' partition key for a Cassandra table seems like it would be 'customer'. This is the primary way we want to query the data, we would get good data distribution, etc. But if there were well over 1 million customers, would that be too many different partitions? Should I choose a partition key that results in a smaller number of partition keys? I've looked at a number of the related questions on this topic but none seem to address this particular point.

问题 Basically, my question is this - I have a list of prices, some of which are historical (i.e. I want to be able to search that product X was $0.99 on March 11, $1.99 on April 1, etc...). What is the best way to store this information? I assumed I would probably have a Product table that has a foreign key to a price table. I initially thought that storing the current price would probably be the best bet, but I think I want to be able to store historical price data, so would the better route to

问题 I have events and photos, and then comments for both. Right now, I have two comments tables, one for comments related to the events, and another for photo comments. Schema is similar to this: CREATE TABLE EventComments ( CommentId int, EventId int, Comment NVarChar(250), DateSubmitted datetime ) CREATE TABLE PhotoComments ( CommentId int, PhotoId int, Comment NVarChar(250), DateSubmitted datetime ) My questions is whether or not I should combine them, and add a separate cross reference table,

问题 I've always created my NSFetchRequests entirely in-code. Now I'm looking at the Xcode GUI for building a fetch request and storing it in the model. I'm following an example from the Xcode Documentation. I added a Fetch Request to my model, and the predicate that has been created through the Modelling GUI is: firstName LIKE[c] "*SUBSTRING*" I then retrieve that request with these two lines: NSDictionary *substituionDictionary = [NSDictionary dictionaryWithObject:@"woody" forKey:@"SUBSTRING"];

问题 Is there some way to model type hierarchies in Neo4j? If for example I want to build a class hierarchy of cars, I might have a base type of "Car" and then have sub classes that extend that, like "SportCar", etc. I'd like to be able to create instances of "SportCar", but run a query to get all "Car"s. Is this possible? If so what is the technique? I think what I'm trying to do is create a "label hierarchy" - but I just don't think that's supported in neo4j. 回答1: Paul, First, I'd recommend that

问题 I'm developing a simple survey module for an ASP application I'm working on and I'd like to get some suggestions on the data model. Questions can be one of three types - multiple choice, multiple answer; multiple choice, single answer, and free response. I'm thinking of the following tables: Question - with a question type discriminator ifeld PossibleAnswers- with a questionID and answer text field SurveyQuestionResponse- with a questionID, a clientID, and answer text Am I making this too