Build elasticsearch query with C-style boolean expression.

see ./query_builder_test.go

The v1.0.0+ version is broken due to a bad commit :(, use v2 instead.

1. import "github.com/r4ve1/esqb/v2"
2. Use the expression to be parsed and a query factory to instanciate a queryBuilder (The queryBuilder will be instanciated only if the expression can be parsed without any problems)
3. The query factory is a 2-level map, which maps field-alias & comparator combinations to queryGenerator (a closure function). When queryGenerator is called, it will return a sub-query for the certain field with the given value.
4. Call the Build() function to finally build the query

When an expression is given, it will:

1. Scan the expression and extract all tokens from it.
2. Use shunting-yard algorithm to convert these tokens to a suffix expression.
3. Parse the expression and return the final query
   • If the operator is a comparing operator and one of the operands is a field-alias, calls the queryGenerator to build a query.
   • If the operator is a logical operator and both of the operands are elastic.Query, use elastic.BoolQuery to group the sub queries.

1. Lexer from govaluate
2. Shunting-yard algorithm from go-shunting-yard