elasticsearch Alias field type 使用注意事项
Alias field type
啥也不说，先附上文档链接
https://www.elastic.co/guide/en/elasticsearch/reference/7.17/field-alias.html#field-alias
本次就做一次 alias 的注意事项笔记，希望对大伙（不爱翻官方文档的）有点帮助(o゜▽゜)o☆[BINGO!]
首先简要描述一下 Alias 。它是别名，为索引中的字段定义替代名称，可以对别名搜索达到搜索映射来源的效果。
注意事项
那么正文开始：
Alias targetsedit
There are a few restrictions on the target of an alias:
The target must be a concrete field, and not an object or another field alias.
目标必须是一个明确的字段，不能是一个object对象或者其它别名。
错误尝试：指定的目标为 object
ps（name目标由于没有指定类型，且是一个json对象，所以是一个object类型）
PUT alias_test
{
"mappings": {
"properties": {
"name_content": {
"type": "alias",
"path": "name"
},
"name": {
"first": "John",
"last": "Smith"
}
}
}
}
*********************result*************************
{
"error" : {
"root_cause" : [
{
"type" : "mapper_parsing_exception",
"reason" : "No type specified for field [name]"
}
],
"type" : "mapper_parsing_exception",
"reason" : "Failed to parse mapping [_doc]: No type specified for field [name]",
"caused_by" : {
"type" : "mapper_parsing_exception",
"reason" : "No type specified for field [name]"
}
},
"status" : 400
}
错误尝试：指定的目标为 其它的别名
由于别名本身并不会作为真实字段进行存储与_source，所以当指定的目标为其它别名时，所报的提示错误会和指定了一个不存在字段的错误信息一致。
PUT alias_test
{
"mappings": {
"properties": {
"name_content": {
"type": "alias",
"path": "name"
},
"name": {
"type": "alias",
"path": "name_content"
}
}
}
}
*********************result*************************
{
"error" : {
"root_cause" : [
{
"type" : "mapper_parsing_exception",
"reason" : "Invalid [path] value [name] for field alias [name_content]: an alias must refer to an existing field in the mappings."
}
],
"type" : "mapper_parsing_exception",
"reason" : "Invalid [path] value [name] for field alias [name_content]: an alias must refer to an existing field in the mappings."
},
"status" : 400
}
The target field must exist at the time the alias is created.
在创建别名时，目标字段必须已经存在。
错误尝试：指定的目标字段不存在
PUT alias_test
{
"mappings": {
"properties": {
"name_content": {
"type": "alias",
"path": "name"
}
}
}
}
*********************result*************************
{
"error" : {
"root_cause" : [
{
"type" : "mapper_parsing_exception",
"reason" : "Invalid [path] value [name] for field alias [name_content]: an alias must refer to an existing field in the mappings."
}
],
"type" : "mapper_parsing_exception",
"reason" : "Invalid [path] value [name] for field alias [name_content]: an alias must refer to an existing field in the mappings."
},
"status" : 400
}
If nested objects are defined, a field alias must have the same nested scope as its target.
如果定义了嵌套对象，则字段别名必须与其目标具有相同的嵌套作用域。
en…这点博主没搞懂，望大伙解惑。
A field alias can only have one target
字段别名只允许有一个目标字段。
错误尝试：字段别名指定数组
它会将你的数组识别成一个目标字段，所以会报找寻不到此字段的错误。
如下，它会把数组识别成 “[name, address]” 字段，若是你有一个字段的名称 为 “[name, address]”，那倒是会添加成功。
PUT alias_test
{
"mappings": {
"properties": {
"name_content": {
"type": "alias",
"path": ["name","address"]
},
"name": {
"type": "keyword"
},
"address": {
"type": "keyword"
}
}
}
}
*********************result*************************
{
"error" : {
"root_cause" : [
{
"type" : "mapper_parsing_exception",
"reason" : "Invalid [path] value [[name, address]] for field alias [name_content]: an alias must refer to an existing field in the mappings."
}
],
"type" : "mapper_parsing_exception",
"reason" : "Invalid [path] value [[name, address]] for field alias [name_content]: an alias must refer to an existing field in the mappings."
},
"status" : 400
}
************************* success ***************************
PUT alias_test
{
"mappings": {
"properties": {
"name_content": {
"type": "alias",
"path": ["name","address"]
},
"[name, address]": {
"type": "keyword"
}
}
}
}
Attempting to use an alias in an index or update request will result in a failure.
试图在索引或更新请求中使用别名将导致失败。
错误尝试：新增数据中，包含别名字段
PUT alias_test
{
"mappings": {
"properties": {
"name_content": {
"type": "alias",
"path": "name"
},
"name": {
"type": "keyword"
}
}
}
}
PUT /alias_test/_doc/1
{
"name": "Benedict Cumberbatch",
"name_content": "handsome"
}
************************* result ***************************
{
"error" : {
"root_cause" : [
{
"type" : "mapper_parsing_exception",
"reason" : "failed to parse"
}
],
"type" : "mapper_parsing_exception",
"reason" : "failed to parse",
"caused_by" : {
"type" : "illegal_argument_exception",
"reason" : "Cannot write to a field alias [name_content]."
}
},
"status" : 400
}
aliases cannot be used as the target of copy_to
aliases 不能当作 copy_to 的目标。
**错误尝试：aliases 被当作了 copy_to 的目标 **
因为 copy_to 的目标必须为存在的字段，而 alias 并不是。
创建索引的时候并不会失败，能创建成功，但是添加数据的时候会失败。
PUT alias_copy_to_test
{
"mappings": {
"properties": {
"name_content": {
"type": "alias",
"path": "name"
},
"name": {
"type": "keyword"
},
"last_name": {
"type": "keyword",
"copy_to": "name_content"
}
}
}
}
PUT alias_copy_to_test/_doc/1
{
"name": "Benedict Cumberbatch",
"name_content": "handsome",
"last_name": "Sherlock"
}
************************* result ***************************
{
"error" : {
"root_cause" : [
{
"type" : "mapper_parsing_exception",
"reason" : "failed to parse"
}
],
"type" : "mapper_parsing_exception",
"reason" : "failed to parse",
"caused_by" : {
"type" : "illegal_argument_exception",
"reason" : "Cannot write to a field alias [name_content]."
}
},
"status" : 400
}
Because alias names are not present in the document source, aliases cannot be used when performing source filtering
由于别名并不是真正存储于_source的字段，所以对_source进行查询是无效的。
PUT alias_test
{
"mappings": {
"properties": {
"name_content": {
"type": "alias",
"path": "name"
},
"name": {
"type": "keyword"
}
}
}
}
PUT /alias_test/_doc/1
{
"name": "Benedict Cumberbatch"
}
GET /alias_test/_search
************************* result ***************************
"hits" : [
{
"_index" : "alias_test",
"_type" : "_doc",
"_id" : "1",
"_score" : 1.0,
"_source" : {
"name" : "Benedict Cumberbatch"
}
}
]
结果并没有别名字段。
end
这次的笔记希望对大伙能有点收获，其中博主也有一个地方不太明白，
If nested objects are defined, a field alias must have the same nested scope as its target.
希望大伙能帮帮忙，解解惑┗|｀0′|┛
|