在ecto assoc加入表中添加where子句

Question

我有三个模型Table1,Table2和Table1to2。 Table1to2从表1联接表，表2，与Table 1和表2是架构：

schema "table1" do 
    many_to_many :table2, Table2, join_through: Table1to2 
end 

schema "table2" do 
    many_to_many :table1, Table1, join_through: Table1to2 
end 

关键的一点是，我的连接表，Table1to2有一栏/场，我需要对查询。从本质上讲，我希望做这样的事情：

Repo.get!(Table1, id) |> Repo.preload(table2: (from j in Table1to2, where: [main: true])) 

这可以理解不起作用，因为没有直接定义的关联从表1至Table1to2。然而，这样做：

Repo.get!(Table1, id) |> Repo.preload(table2: (from j in Table2, where: [main: true])) 

结果在此查询：

from p0 in Table1, 
    join: u in Table1to2, 
    on: u.table1_id == p0.id, 
    join: p1 in Table2, 
    on: u.table2_id == p1.id, 
    where: p1.main == true,  #should be u.main == true 
    where: p0.id == ^"2", 
    select: p0, 
    preload: [table_2: p1] 

Answer 1

您可以随时使用的查询语法像你发布到满足您的需要生成的查询。

query = 
    from t1 in Table1, 
    join: t12 in Table1to2, on: t12.table1_id == t1.id, 
    join: t2 in Table2, on: t12.table2_id == t2.id, 
    where: t12.main == :true and t1.id == ^table1_id, 
    preload: [table2: t1], 
    select: t1 

result = Repo.one(query)