compound-key

来源： https://stackoverflow.com/questions/29212691/how-to-merge-two-dataframes-using-multiple-columns-as-key

来源： https://stackoverflow.com/questions/29212691/how-to-merge-two-dataframes-using-multiple-columns-as-key

问题 I'm trying to use Spring Data JDBC to access a table that has a compound key, and although I can find lots of info on how Spring Data JPA handles this, the same doesn't seem to apply to Spring Data JDBC. Can anyone give a quick example of how you need to declare an Entity/Repository with Spring Data JDBC to talk to a table with a compound primary key ? (Eg. Two Strings) 回答1: Using the CrudRepository for compound keys is currently (Version 1.0.2) not possible. Of course, you can still use

问题 I am trying to calculate the hourly mean of x in a data frame similar to this: min hour day month year x 1 10 22 31 12 2013 18.3 2 30 22 31 12 2013 16.5 3 50 22 31 12 2013 15.7 4 10 23 31 12 2013 16.7 5 30 23 31 12 2013 18.0 6 50 23 31 12 2013 18.1 7 10 0 1 1 2014 17.4 8 30 0 1 1 2014 15.4 9 50 0 1 1 2014 16.9 I have tried different things with the aggregate function but without luck. So what I want is to calculate the mean of x if the value of hour , day , month , year are the same. The

问题 I have the following EF Code First classes, which appear to be working to a point. I also have Initialization code that seeds these tables with data from elsewhere that is lengthy, and seems (I hope) inconsequential to my question. Or at the least when I seed manually I see the same behavior problem. Note, that these tables use strings as their primary keys, and not ID's. Also note that the SubCategory table has a compound primary key that includes the parent table, Category's primary key,

问题 I've read that compound primary keys will confuse the hell out of typical ORM code generators. Which ORMs work best with compound PKs and which to avoid? (I've a particular interest in .NET) 回答1: I'm using NHibernate successfully with compound keys. <class name="UserProfileField" table="UserProfileFields"> <composite-id> <key-many-to-one name="Parent" column="UserId" lazy="false"/> <key-property name="FieldName"/> </composite-id> ... 来源： https://stackoverflow.com/questions/218100/orm-support

问题 I've read that compound primary keys will confuse the hell out of typical ORM code generators. Which ORMs work best with compound PKs and which to avoid? (I've a particular interest in .NET) 回答1: I'm using NHibernate successfully with compound keys. <class name="UserProfileField" table="UserProfileFields"> <composite-id> <key-many-to-one name="Parent" column="UserId" lazy="false"/> <key-property name="FieldName"/> </composite-id> ... 来源： https://stackoverflow.com/questions/218100/orm-support

问题 I've got database tables like this: A person may be a member of many teams. A team may have many members. Each person may have a position (think job title) within the team. I've tried to set this up with ADO.NET Entity Framework and get errors: Error 3021: Problem in mapping fragments starting at line ... Each of the following columns in table Membership is mapped to multiple conceptual side properties: Membership.PersonId is mapped to <MembershipPerson.Membership.PersonId, MembershipPerson

问题 In a legacy database, I have three tables: Users, Workgroups, and UsersWorkgroup. UsersWorkgroup stores what role a user has in a workgroup. Here are the relevant code snippets: @Entity @Table(name = "users_workgroup") public class UsersWorkgroup implements Serializable { private static final long serialVersionUID = 1L; @EmbeddedId protected UsersWorkgroupPK usersWorkgroupPK; @JoinColumn(name = "idworkgroup", referencedColumnName = "idworkgroup") @ManyToOne(optional = false) private Workgroup

问题 I would like to run the following code with a compound primary key. Column<String> result = keyspace.prepareQuery(CF_COUNTER1) .getKey(rowKey) .getColumn("Column1") .execute().getResult(); Long counterValue = result.getLongValue(); Research seems to show that it can be a string that represents a key (if it's not a compound primary key). The documentation says that it is of type K , alas, I am not very experience with Java, and have no idea what that means. Is it just a base type that lots of