我有一个标准的 ruby 包含,smth。像那样:
@properties = Property.where(id: property_ids)
.includes(:property_values).select('select distinct "property_values"."value"').references(:property_values)
我需要每个属性属性值的唯一值。
但是对于这个查询得到一个错误:
PG::SyntaxError - ERROR: syntax error at or near "select"
LINE 1: ...S t1_r4, "property_values"."updated_at" AS t1_r5, select dis...
这里是完整的查询:
: SELECT "properties"."id" AS t0_r0, "properties"."k1c" AS t0_r1, "properties"."name" AS t0_r2, "properties"."created_at" AS t0_r3, "properties"."updated_at" AS t0_r4, "property_values"."id" AS t1_r0, "property_values"."value" AS t1_r1, "property_values"."product_id" AS t1_r2, "property_values"."property_id" AS t1_r3, "property_values"."created_at" AS t1_r4, "property_values"."updated_at" AS t1_r5, select distinct "property_values"."value" FROM "properties" LEFT OUTER JOIN "property_values" ON "property_values"."property_id" = "properties"."id" WHERE "properties"."id" IN (159, 27, 26, 25, 24, 23, 22, 4, 1) AND "properties"."id" IN (1) ORDER BY "properties"."id" ASC
如何避免此错误并仅获取唯一属性值?
最佳答案
@properties = Property.where(id: property_ids)
.joins(:property_values).select('"property_values"."value"').distinct.references(:property_values)
请注意,我将 includes
更改为连接,因为 includes
在单独的查询中加载数据,而 join
实际上执行连接,允许您执行对查询中的数据执行操作..
我使用了 distinct 方法而不是将其放在 select 中,但是您可以这样做,但是您需要从字符串中删除 select 一词
@properties = Property.where(id: property_ids)
.joins(:property_values).select('distinct "property_values"."value"').references(:property_values)
阅读更多 http://blog.bigbinary.com/2013/07/01/preload-vs-eager-load-vs-joins-vs-includes.html
关于sql - rails 包含不同的值,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/23623633/