两张表:
var query = db.Categories // 第一张表
.Join(db.CategoryMaps, // 第二张表
c => c.CategoryId, // 主键
cm => cm.ChildCategoryId, // 外键
(c, cm) => new { Category = c, CategoryMap = cm }) // 关联后的结果对象集
.Select(x => x.Category); // select 查询结果集
多张表:
var fullEntries = dbContext.tbl_EntryPoint //第一张表
.Join(
dbContext.tbl_Entry, //第二张表
entryPoint => entryPoint.EID,
entry => entry.EID,
(entryPoint, entry) => new { entryPoint, entry }
)
.Join(
dbContext.tbl_Title, //第三张表
combinedEntry => combinedEntry.entry.TID,
title => title.TID,
(combinedEntry, title) => new
{
UID = combinedEntry.entry.OwnerUID,
TID = combinedEntry.entry.TID,
EID = combinedEntry.entryPoint.EID,
Title = title.Title
}
)
.Where(fullEntry => fullEntry.UID == user.UID)
.OrderBy(p=>p.UID)
.Take();
优点:coding方便
缺点:join多张表的情景,代码冗长
替代方法:创建数据库视图,对视图进行EF查询