.NET Core利用BsonDocumentProjectionDefinition和Lookup进行 join 关联查询(推荐)
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前段时间由于项目需要用到MongoDB,但是MongoDB不建议Collection join 查询,网上很多例子查询都是基于linq 进行关联查询。但是在stackoverflow找到一个例子,程序员的朋友们请善于利用google搜索。主要介绍一个查询角色的所有用户的例子。MongoDB创建Collection 和准备数据,请自行处理。
1. 准备实体模型
/// <summary> /// 用户实体(Collection) /// </summary> public class User { public Guid UserId { get; set; } public string UserName { get; set; } public string Password { get; set; } public bool IsDelete { get; set; } public DateTime CreateTime { get; set; } public Guid RoleId { get; set; } } /// <summary> /// 角色实体(Collection) /// </summary> public class Role { public Guid RoleId { get; set; } public string RoleName { get; set; } public DateTime CreateTime { get; set; } } /// <summary> /// 构建用户Dto(不在Mongo创建Collection) /// </summary> public class UserDto { public Guid UserId { get; set; } public string UserName { get; set; } public DateTime CreateTime { get; set; } public Guid RoleId { get; set; } public string RoleName { get; set; } }
2 .前置连接Mongo代码
var client = new MongoClient("xxx"); var database = client.GetDatabase("xxx");
3. 构建BsonDocumentProjectionDefinition
BsonDocumentProjectionDefinition<BsonDocument> projectionDefinition = new BsonDocumentProjectionDefinition<BsonDocument>( new BsonDocument("UserId", "$UserId") .Add("UserName", "$UserName") .Add("CreateTime", "$CreateTime") .Add("RoleId", "$RoleId") .Add("RoleName", new BsonDocument("$arrayElemAt", new BsonArray().Add("$Role.RoleName").Add(0))) );
4.利用 Lookup 进行关联
Guid roleId = Guid.Empty; List<UserDto> list = database.GetCollection<BsonDocument>(typeof(User).Name) .Aggregate() //过滤条件 .Match(Builders<BsonDocument>.Filter.Eq("IsDelete", false)) .Match(Builders<BsonDocument>.Filter.Eq("RoleId", roleId)) //连接Role .Lookup(typeof(Role).Name, "RoleId", "RoleId", typeof(UserDto).Name) //查询需要显示的列 .Project(projectionDefinition) .As<UserDto>().ToList();
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