本文基于es7.1版本。node
针对空值的测试，使用了以下几种值：null、“null”、“”、[ ];数据库
测试代码太长，先说结论，对于全部类型，null、“”、[ ]都可以被索引，可是没法检索。对于部分数据类型，因为“null”不能转换为对应的类型，所以索引时会报错，可是对于keywork、text等能够索引string类型的字段，“null”被视做普通的string，可被索引与检索。不能够被直接检索的缘由，套用es权威指南中的一句原话： If a field has no values, how is it stored in an inverted index?现实是，空值字段在倒排索引中没有存储，it isn’t stored at all。json
须要注意的是，若是是基于es2.x版本，可以使用exists，或者missing来检索非null/null值。分别等同于关系数据库中的is not null 和is null。可是missing在7.1版本中已不可用。直接使用会报错：“no [query] registered for [missing]”。数组
在程序设计时，为了给null值设置默认值，可以使用null_value属性。相似于关系数据库中的default默认值，但又有不一样，这个请继续往下看第3点。可是须要注意的是，以下三点：app
1，在es中，只有显示设置null时，null_value才会生效，设置空数组如[ ]，空字符串如""均不生效。
2，null_value默认值应该匹配数据类型。例如，date类型不能设置字符串默认值。
3，null_value仅可让字段以null_value值被倒排索引存储，以即可以让此文档被检索。并不会替换_source中的实际json文档值。测试
建立测试对象：ui
PUT ac_blog1
{
"mappings": {
"properties": {
"title":{
"type": "text"
},
"body":{
"type": "text"
},
"author":{
"type": "keyword"
},
"views":{
"type": "long"
}
}
}
}
录入数据：设计
POST ac_blog1/_doc
{
"views":null
}
POST ac_blog1/_doc
{
"views":[]
}
POST ac_blog1/_doc
{
"views":""
}
测试一下，获取所有数据：code
GET ac_blog1/_search
{
"query": {
"match_all": {}
},
"size":100
}
响应：orm
{
"took" : 355,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 3,
"relation" : "eq"
},
"max_score" : 1.0,
"hits" : [
{
"_index" : "ac_blog1",
"_type" : "_doc",
"_id" : "HFBiSW0Bf1cVbYphJHEo",
"_score" : 1.0,
"_source" : {
"views" : null
}
},
{
"_index" : "ac_blog1",
"_type" : "_doc",
"_id" : "HVBiSW0Bf1cVbYphPHEa",
"_score" : 1.0,
"_source" : {
"views" : [ ]
}
},
{
"_index" : "ac_blog1",
"_type" : "_doc",
"_id" : "HlBiSW0Bf1cVbYphRXGX",
"_score" : 1.0,
"_source" : {
"views" : ""
}
}
]
}
}
可见文档数据都已被索引。下面来查一下：
测试null的状况：
GET ac_blog1/_search
{
"query": {
"term": {
"views":null
}
}
}
响应：
{
"error": {
"root_cause": [
{
"type": "illegal_argument_exception",
"reason": "field name is null or empty"
}
],
"type": "illegal_argument_exception",
"reason": "field name is null or empty"
},
"status": 400
}
测试[ ]的状况：
GET ac_blog1/_search
{
"query": {
"term": {
"views":[]
}
}
}
响应：
{
"error": {
"root_cause": [
{
"type": "parsing_exception",
"reason": "[term] query does not support array of values",
"line": 4,
"col": 15
}
],
"type": "parsing_exception",
"reason": "[term] query does not support array of values",
"line": 4,
"col": 15
},
"status": 400
}
测试""的状况：
GET ac_blog1/_search
{
"query": {
"term": {
"views":""
}
}
}
响应：
{
"error": {
"root_cause": [
{
"type": "query_shard_exception",
"reason": "failed to create query: {\n \"term\" : {\n \"views\" : {\n \"value\" : \"\",\n \"boost\" : 1.0\n }\n }\n}",
"index_uuid": "f_2YYPS6RAaew5bXcQwlzQ",
"index": "ac_blog1"
}
],
"type": "search_phase_execution_exception",
"reason": "all shards failed",
"phase": "query",
"grouped": true,
"failed_shards": [
{
"shard": 0,
"index": "ac_blog1",
"node": "oJRDxfVrQlGOJ9eqCGozDg",
"reason": {
"type": "query_shard_exception",
"reason": "failed to create query: {\n \"term\" : {\n \"views\" : {\n \"value\" : \"\",\n \"boost\" : 1.0\n }\n }\n}",
"index_uuid": "f_2YYPS6RAaew5bXcQwlzQ",
"index": "ac_blog1",
"caused_by": {
"type": "number_format_exception",
"reason": "empty String"
}
}
}
]
},
"status": 400
}
由于views为null类型，没法测试“null”的状况，会报错null没法转换为long类型，这个显而易见是es作的处理，并非底层lucene的功能。换用keyword类型的author来测试：
POST ac_blog1/_doc
{
"author":"null"
}
GET ac_blog1/_search
{
"query": {
"term": {
"author":"null"
}
}
}
响应：
{
"took" : 416,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 1,
"relation" : "eq"
},
"max_score" : 0.2876821,
"hits" : [
{
"_index" : "ac_blog1",
"_type" : "_doc",
"_id" : "H1BoSW0Bf1cVbYphtHF9",
"_score" : 0.2876821,
"_source" : {
"author" : "null"
}
}
]
}
}
以上。