英文:
gocraft/dbr: How to JOIN with multiple conditions?
问题
我使用golang开发Web应用程序。
我使用gocraft/dbr库作为O/R映射器。
我有两个表：image和entry。
我将它们的表连接起来，我想获取image_url。
type Image struct {
ImageUrl dbr.NullString `db:"image_url"`
}
type Entry struct {
CompanyImageID dbr.NullInt64 `db:"company_image_id"`
CompanyImage Image
EyecatchIamgeID dbr.NullInt64 `db:"eyecatch_image_id"`
EyecatchImage Image
}
然后我尝试了以下代码：
var entry Entry
sess.Select("*").From("entry").
LeftJoin(dbr.I("image").As("eyecatch_image"), "entry.eyecatch_image_id = eyecatch_image.id").
LeftJoin(dbr.I("image").As("company_image"), "entry.company_image_id = company_image.id").
Load(&entry)
log.Println("company:", entry.CompanyImage)
log.Println("eyecatch:", entry.EyecatchImage)
结果为：
company: {{{https://company_image_url.png true}}}
eyecatch: {{{ false}}}
我期望的结果是：
company: {{{https://company_image_url.png true}}}
eyecatch: {{{{http://eyecatch_image_url.png true}}}
当我尝试更改连接条件如下所示时：
sess.Select("*").From("entry").
LeftJoin(dbr.I("image").As("eyecatch_image"), "entry.eyecatch_image_id = eyecatch_image.id").
Load(&entry)
结果为：
company: {{{http://eyecatch_image_url.png true}}}
eyecatch: {{{ false}} {{ false}}}}
我不知道如何在多个条件下使用连接。
谢谢。
英文:
I develop web application with golang.
I use the library gocraft/dbr as O/R Mapper.
I have two tables: image and entry.
I join their tables and I want to get image_url.
type Image struct {
ImageUrl dbr.NullString `db:"image_url"`
}
type Entry struct {
CompanyImageID dbr.NullInt64 `db:"company_image_id"`
CompanyImage Image
EyecatchIamgeID dbr.NullInt64 `db:"eyecatch_image_id"`
EyecatchImage Image
}
Then I tried below:
var entry Entry
sess.Select("*").From("entry").
LeftJoin(dbr.I("image").As("eyecatch_image"), "entry.eyecatch_image_id = eyecatch_image.id").
LeftJoin(dbr.I("image").As("company_image"), "entry.company_image_id = company_image.id").
Load(&entry)
log.Println("company:", entry.CompanyImage)
log.Println("eyecatch:", entry.EyecatchImage)
result:
company: {{{https://company_image_url.png true}}}
eyecatch: {{{ false}}}
I expect below, but it did not become as expected.
company: {{{https://company_image_url.png true}}}
eyecatch: {{{{http://eyecatch_image_url.png true}}}
When I tried to change join condition like below:
sess.Select("*").From("entry").
LeftJoin(dbr.I("image").As("eyecatch_image"), "entry.eyecatch_image_id = eyecatch_image.id")
Load(&entry)
result:
company: {{{http://eyecatch_image_url.png true}}}
eyecatch: {{{ false}} {{ false}}}}
I don't know how to use join with multiple conditions.
Thank you.
答案1
得分: 1
文档真的很差劲 - 似乎他们放弃了发布这个库的想法。有一个开放的拉取请求提供了稍微好一点的文档。 在这里，作者描述了如何创建一个多条件的示例：
cond:= dbr.And(
dbr.Or(
dbr.Gt("created_at", "2015-09-10"),
dbr.Lte("created_at", "2015-09-11"),
),
dbr.Eq("title", "hello world"),
)
然后在任何语句中使用这个条件：
sess.Select("*").From("entry").
LeftJoin(dbr.I("image").As("eyecatch_image"), cond)
Load(&entry)
英文:
The documentation is really poor - it seems they gave up on the idea of publishing the library. There is an open pull request that provides a little better documentation.. Here the author describes that you can create a multiple condition like this:
cond:= dbr.And(
dbr.Or(
dbr.Gt("created_at", "2015-09-10"),
dbr.Lte("created_at", "2015-09-11"),
),
dbr.Eq("title", "hello world"),
)
Then use the condition in any statement:
sess.Select("*").From("entry").
LeftJoin(dbr.I("image").As("eyecatch_image"), cond)
Load(&entry)
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