答案 0 :(得分：8)
好问题。典型的多对多关系只是两个一对多的关系：
任何实现中更重要的细节之一是：在哪里 关系信息存储？这个问题的答案决定了如何 可以访问实体的关系。让我们探讨一些选择。
前提：
A hasMany B
B hasMany A
选项1
关系信息存储在A。
在这种情况下，一旦你有一个A的实例，你就可以找到它的关联
B的实例，因为存储了关联的B实例的ID
A。这也意味着，如果您只有B的实例，那么这是唯一的方法
找到A实例所涉及的B的所有实例
搜索A字段包含b_ids字段的id的所有实例
B实例的var Player = store.defineResource({
name: 'player',
relations: {
hasMany: {
team: {
// JSData will setup a "teams" property accessor on
// instances of player which searches the store for
// that player's teams
localField: 'teams',
localKeys: 'team_ids'
}
}
}
})
var Team = store.defineResource({
name: 'team',
relations: {
hasMany: {
player: {
localField: 'players',
// Since relationship information is stored
// on the player, in order to retrieve a
// team's players we have to do a O(n^2)
// search through all the player instances
foreignKeys: 'team_ids'
}
}
}
})
。
一个例子
var player = Player.inject({
id: 1,
team_ids: [3, 4]
})
// The player's teams aren't in the store yet
player.teams // [ ]
var player2 = Player.inject({
id: 2,
team_ids: [4, 5],
teams: [
{
id: 4
},
{
id: 5
}
]
})
// See the property accessor in action
player2.teams // [{ id: 4 }, { id: 5 }]
// One of player one's teams is in the store now
player.teams // [{ id: 4 }]
// Access the relation from the reverse direction
var team4 = Team.get(4) // { id: 4 }
// The property accessor makes a O(n^2) search of the store because
// the relationship information isn't stored on the team
team4.players // [{ id: 1, team_ids: [3, 4] }, { id: 2, team_ids: [4, 5] }]
现在让我们看看它的实际效果：
// To get an authoritative list of player one's
// teams we ask our persistence layer.
// Using the HTTP adapter, this might make a request like this:
// GET /team?where={"id":{"in":[3,4]}} (this would be url encoded)
//
// This method call makes this call internally:
// Team.findAll({ where: { id: { 'in': player.team_ids } } })
player.DSLoadRelations(['team']).then(function (player) {
// The adapter responded with an array of teams, which
// got injected into the datastore.
// The property accessor picks up the newly injected team3
player.teams // [{ id: 3 }, { id: 4 }]
var team3 = Team.get(3)
// Retrieve all of team3's players.
// Using the HTTP adapter, this might make a request like this:
// // GET /player?where={"team_ids":{"contains":3}} (this would be url encoded)
//
// This method call makes this call internally:
// Player.findAll({ where: { team_ids: { 'contains': team3.id } } })
return team3.DSLoadRelations(['player'])
})
让我们从持久层加载关系：
B如果您正在使用HTTP适配器，那么它可以直接到您的服务器来解析 查询字符串并使用正确的数据进行响应。如果你正在使用任何一个 其他适配器然后适配器已经知道如何返回正确的数据。 在前端和后端使用JSData只会让这很容易。
选项2
关系信息存储在A。
这只是选项1 的反面。
选项3
＆＃34; B hasMany A＆＃34;关系信息存储在实例B上，和
＆＃34; A hasMany B＆＃34;关系信息存储在foreignKeys。
这只是选项1 ，但它现在可以双向工作。
这种方法的一个优点是您可以从两者访问关系
方向，无需使用A选项。一个缺点
这种方法是当关系发生变化时必须修改数据
多个地方。
选项4
关系信息存储在数据透视（联结）表中。
C hasMany C和A belongsTo C，其实际关系
信息存储在B。
C hasMany C和B belongsTo C，其实际关系
信息存储在var Player = store.defineResource({
name: 'player',
relations: {
hasMany: {
membership: {
localField: 'memberships',
// relationship information is stored on the membership
foreignKey: 'player_id'
}
}
}
})
var Team = store.defineResource({
name: 'team',
relations: {
hasMany: {
membership: {
localField: 'memberships',
// relationship information is stored on the membership
foreignKey: 'team_id'
}
}
}
})
。
一个例子：
var Membership = store.defineResource({
name: 'membership',
relations: {
belongsTo: {
player: {
localField: 'player',
// relationship information is stored on the membership
localKey: 'player_id'
},
team: {
localField: 'team',
// relationship information is stored on the membership
localKey: 'team_id'
}
}
}
})
枢轴资源：
var player = Player.inject({ id: 1 })
var player2 = Player.inject({ id: 2 })
var team3 = Team.inject({ id: 3 })
var team4 = Team.inject({ id: 4 })
var team4 = Team.inject({ id: 5 })
player.memberships // [ ]
player2.memberships // [ ]
team3.memberships // [ ]
team4.memberships // [ ]
team5.memberships // [ ]
现在让我们看看它的实际效果：
// The relationships stored in our pivot table
var memberships = Membership.inject([
{
id: 997,
player_id: 1,
// player one is on team three
team_id: 3
},
{
id: 998,
player_id: 1,
// player one is also on team four
team_id: 4
},
{
id: 999,
player_id: 2,
// team four also has player 2
team_id: 4
},
{
id: 1000,
player_id: 2,
// player 2 is also on team 5
team_id: 5
}
])
请注意，此时我们无法访问任何关系
player.memberships // [{ id: 997, ... }, { id: 998, ... }]
player2.memberships // [{ id: 998, ... }, { id: 999, ... }]
team3.memberships // [{ id: 997, ... }]
team4.memberships // [{ id: 998, ... }, { id: 999, ... }]
team5.memberships // [{ id: 1000, ... }]
现在我们有会员资料
var Player = store.defineResource({
name: 'player',
relations: {...},
computed: {
teams: {
get: function () {
return store.filter('membership', {
player_id: this.id
}).map(function (membership) {
return store.get('team', membership.team_id)
})
}
}
},
// Instance methods
methods: {
getTeams: function () {
return Player.getTeams(this.id)
}
}
// Static Class Methods
getTeams: function (id) {
return this.loadRelations(id, ['membership']).then(function (memberships) {
return store.findAll('team', {
where: {
id: {
'in': memberships.map(function (membership) {
return membership.team_id
})
}
}
})
})
}
})
现在，将您的数据透视表数据发送到您的前端并且有点笨拙 要求你的JavaScript对关系进行排序。为此你想要的 一些辅助方法：
static void InsertTextInCell(WorksheetPart worksheetPart)
{
Worksheet workSheet = worksheetPart.Worksheet;
SheetData sheetData = workSheet.GetFirstChild<SheetData>();
Cell cell = new Cell()
{
CellReference = "E8",
DataType = CellValues.String,
CellValue = new CellValue("Adding Value")
};
sheetData.Append(cell);
}
我会让你弄清楚团队资源的类似方法。
如果你不想解决辅助方法的麻烦，那么你可能会 只需在后端实现它们，使您的数据透视表不可见 前端并使你的多对多关系看起来更像是选项1,2或 3。
有用的链接