根据参数添加内连接或外连接

Question

这可能是一个简单/愚蠢的问题，但他们是否可以根据您收到的数据将内部或外部联接添加到 SQL 查询（使用实体框架）？

示例

public bool method(int? typeId, int? categoryId){
    var query = from o in _dbContext.SomeObjects;

    //JOIN type
    if(typeId != null){
        //Add inner join with table types to query
        //Something like:  
        //query += join type in _dbContext.Types on o.TypeId equals type.ID
    }else{
        //Add outer join with table types to query
        //query += join type in _dbContext.Types on o.TypeId equals type.ID into types
        //             from type in types.DefaultIfEmpty()
    } 

    //Do same for category
    ...

    //Filters
    if(typeId != null){
        query += where type.ID == typeId
    }

    if(categoryId != null){
        query += where category.ID == categoryId
    }

}

Answer 1

通过执行以下操作修复它：

var query = from o in _dbContext.SomeObjects
                join type in _dbContext.Types on o.TypeId equals type.ID
            where (typeId == null || type.ID == typeId) &&

Answer 2

我认为您的主要问题只是打字。使用var 存储初始查询会将其键入为DbSet<SomeObject>。要构建查询，您需要IQueryable<SomeObject>。换句话说，将您的初始行更改为：

IQueryable<SomeObject> query = from o in _dbContext.SomeObjects;

我自己不使用 LINQ-to-SQL，所以这可能有点不对劲，但我认为您只需执行以下操作：

query = query join type in _dbContext.Types on o.TypeId equals type.ID;

我知道它适用于 LINQ-to-Entities，例如：

query = query.Include(x => x.Types);