Elasticsearch mappings小结

type为string类型的mapping的最重要的两个属性是index和analyzer.
index与三种可选项：
analyzed

First analyze the string and then index it. In other words, index this
field as full text.

not_analyzed

Index this field, so it is searchable, but index the value exactly as
specified. Do not analyze it.

no

Don’t index this field at all. This field will not be searchable

默认值是analyzed，因此如果我们想精确搜索时，需要改为not_analyzed.
对于analyzed的string field,可以使用analyzer 制定搜索和检索时使用的analyzer类型。默认使用standard类型，也可以使用whitespace, simple, 或english。值得注意的是，更新mappings时，可以添加新的fields,但是不能将analyzed改为not_analyzed.
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