orm

How to make an Inner Join in django?

由 ﹥＞﹥吖頭↗ 提交于 2020-01-12 15:26:45
问题 I want to show in an Html the name of the city, state, and country of a publication. But they are in different tables. Here is my models.py class country(models.Model): country_name = models.CharField(max_length=200, null=True) country_subdomain = models.CharField(max_length=3, null=True) def __str__(self): return self.country_name class countrystate(models.Model): state_name = models.CharField(max_length=200, null=True) country = models.ForeignKey(country, on_delete=models.CASCADE, null=True

How to make an Inner Join in django?

由 蓝咒 提交于 2020-01-12 15:26:08
问题 I want to show in an Html the name of the city, state, and country of a publication. But they are in different tables. Here is my models.py class country(models.Model): country_name = models.CharField(max_length=200, null=True) country_subdomain = models.CharField(max_length=3, null=True) def __str__(self): return self.country_name class countrystate(models.Model): state_name = models.CharField(max_length=200, null=True) country = models.ForeignKey(country, on_delete=models.CASCADE, null=True

分享自己的超轻量级高性能ORM数据访问框架Deft

由 生来就可爱ヽ(ⅴ＜●) 提交于 2020-01-12 13:55:46
Deft 简介 Deft是一个超轻量级高性能O/R mapping数据访问框架，简单易用，几分钟即可上手。 Deft包含如下但不限于此的特点： 1、按照Transact-SQL的语法语义风格来设计，只要调用者熟悉基本的Transact-SQL语法即可瞬间无忧开码，大大降低了学习Deft的成本，甚至零成本。 2、性能十分不错（个人觉得易用性很重要，只要性能不拖后腿就好了），通过缓存+Emit反射IDataReader，极速获取List<T>。 3、强大的查询功能，支持使用Lambda表达式任意组装where条件,支持各种各样的运算符和括号优先级，支持给查询字段取别名。 4、支持SQLServer、MySQL、Oracle、SQLite等多数据库类型，同时也支持一个业务系统里面存在多个数据库。 5、支持事务、分页查询、排序等。 6、支持like,in等sql操作符，支持avg,count,max,min,sum等sql函数。 7、颜值高，整套语法接口设计的十分巧妙，支持Lambda 表达式，链式编程，任意组装sql，极度美观。 8、支持手写sql， List<T> Select<T>(string sql)。 9、各种映射能力，包括任意查询的结果映射，支持dynamic。 10、实体类非常简单，手写即可，不需要借助工具，也没有特性标记或者继承BaseEntity等杂七杂八的东西。 11

How is the “Owning Side” of this many-to-many relationship determined?

由 筅森魡賤 提交于 2020-01-12 07:29:46
问题 I'm trying to get a firm grasp on the concept of Owning-side. Couldn't really get a clear picture from any question i found here. Basically I'm going through the Java EE JPA tutorial. They have the following database schema, where PLAYER and TEAM have a many-to-many relationship Also stated A player can be on many teams. A team can have many players. There is a many-to-many relationship between PLAYER and TEAM . Pretty straight forward so far. But when is gets to the coding part, they make

Laravel Eloquent with()-> returning null

由 拟墨画扇 提交于 2020-01-12 07:20:11
问题 I am trying to use Eloquent to get a specific product that has a brand_id column that maps to a brands table, the brand array is coming back empty. Is there anything obvious here that needs to be changed? $product = Product::with('images')->with('brand')->select($fields)->where('display', '=', 1)->find($id); //Product model class Product extends Eloquent { ... public function brand() { return $this->belongsTo('Brand'); } //Brand model class Brand extends Eloquent { ... public function

ORM and SOA in the .NET world

由 爷，独闯天下 提交于 2020-01-12 07:10:59
问题 From my experience the major ORM frameworks for .NET (NHibernate, LinqToSql, Entity Framework) work best when they keep track of loaded objects. This works fine for simple client-server applications, but when using three- or more tier architecture with Web Services in a Service Oriented Archtitecture, this is not possible. Eventually, by writing a lot of code to do the tracking yourself it could be done, but isn't ORM supposed to simplify DB access? Is the idea to use ORM in service oriented

ORM and SOA in the .NET world

由 可紊 提交于 2020-01-12 07:09:27
问题 From my experience the major ORM frameworks for .NET (NHibernate, LinqToSql, Entity Framework) work best when they keep track of loaded objects. This works fine for simple client-server applications, but when using three- or more tier architecture with Web Services in a Service Oriented Archtitecture, this is not possible. Eventually, by writing a lot of code to do the tracking yourself it could be done, but isn't ORM supposed to simplify DB access? Is the idea to use ORM in service oriented

How can I use the F() object to do this with the Django ORM?

由 一个人想着一个人 提交于 2020-01-12 05:34:26
问题 I encountered a model like this: class Task(models.Model): timespan = models.IntegerField(null=True, blank=True) class Todo(models.Model): limitdate = models.DateTimeField(null=True, blank=True) task = models.ForeignKey(Task) I need to extract all Todos with a limitdate that is lower or equal to today's date + a timespan defined in the related Task model. Something like (dummy example): today = datetime.datetime.now() Todo.objects.filter(limitdate__lte=today + F('task__timespan')) Now, I can

Removing child from collection using JPA

由 倾然丶 夕夏残阳落幕 提交于 2020-01-12 02:58:07
问题 I'm using JPA over Hibernate in my web-app. Here are two entities (only getters are shown): class Child { private Parent parent; @ManyToOne(optional=false) @JoinColumn(name="parent_id", referencedColumnName="parent_id", nullable=false, updatable=false) public Parent getParent() { return parent; } } class Parent { private Collection<Child> children; @OneToMany(fetch=FetchType.EAGER, mappedBy="parent", cascade={CascadeType.ALL}) public Collection<Child> getChildren() { return children; } } As

SQL portability gotchas

由 心已入冬 提交于 2020-01-11 19:53:52
问题 My company has me working on finishing a back end for Oracle for a Python ORM. I'm amazed at how much differently RDBMSes do things even for the simple stuff. I've learned a lot about the differences between Oracle and other RDBMSes. Just out of sheer curiosity, I'd like to learn more. What are some common "gotchas" in terms of porting SQL from one platform to another? Please, only one gotcha per answer. 回答1: Oracle does not seem to have a problem with cursors, they are a huge performance
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