Building a Filter Query Parser and Generator in JavaScript: A Jira-like JQL Query Solution

To create a filter query like Jira’s JQL query and parser and generator functions in JavaScript, you can follow the steps below:

Step 1: Define the Query Syntax

First, define the syntax for the filter query. You can use the JQL query syntax as a reference and define your own syntax based on your needs. For example, the syntax can include fields, operators, values, and logical operators like AND and OR.

Here’s an example syntax for a filter query:

(field1: value1) AND (field2: value2 OR field3: value3)

Step 2: Create the Parser Function

Next, create a parser function that can parse the filter query string and generate an object that represents the query. You can use regular expressions to match the syntax of the query string and extract the field, operator, and value components.

Here’s an example parser function that can parse the filter query:

function parseFilterQuery(queryString) {
  const fieldRegex = /([a-zA-Z0-9_]+):/;
  const operatorRegex = /([a-zA-Z]+)\s*:/;
  const valueRegex = /:\s*(.*)$/;
  const tokens = queryString.split(/\s+/);
  let i = 0;
  function parseToken() {
    const token = tokens[i++];
    const fieldMatch = token.match(fieldRegex);
    const operatorMatch = token.match(operatorRegex);
    const valueMatch = token.match(valueRegex);
    if (fieldMatch) {
      const field = fieldMatch[1];
      const operator = operatorMatch ? operatorMatch[1] : "equals";
      const value = valueMatch ? valueMatch[1] : null;
      return { type: "field", field, operator, value };
    } else if (token === "AND" || token === "OR") {
      return { type: "logical", operator: token };
    } else {
      throw new Error(`Invalid token: ${token}`);
    }
  }
  function parseExpression() {
    const tokens = [];
    while (i < tokens.length) {
      const token = parseToken();
      if (token.type === "logical") {
        return tokens;
      } else {
        tokens.push(token);
      }
    }
    return tokens;
  }
  const expressions = [];
  while (i < tokens.length) {
    expressions.push(parseExpression());
  }
  return expressions;
}

This parser function takes a filter query string as input and returns an array of expressions, where each expression is an array of tokens that represents a single field/value pair or a logical operator.

For example, the following filter query string:

(field1: value1) AND (field2: value2 OR field3: value3)

will be parsed into the following array of expressions:

[
  [
    { type: "field", field: "field1", operator: "equals", value: "value1" }
  ],
  [
    { type: "logical", operator: "AND" },
    { type: "field", field: "field2", operator: "equals", value: "value2" },
    { type: "logical", operator: "OR" },
    { type: "field", field: "field3", operator: "equals", value: "value3" }
  ]
]

Step 3: Create the Generator Function

Next, create a generator function that can take the object representation of the filter query and generate the filter query string.

Here’s an example generator function that can generate the filter query string:

function generateFilterQuery(expressions) {
  function generateExpression(expression) {
    return expression.map((token) => {
      if (token.type === "logical") {
        return token.operator;
      } else {
        const operator = token.operator === "equals" ? "" : `${token.operator}:`;
        const value = token.value ? ` ${token.value}` : "";
        return `${token.field}${operator}${value}`;
      }
    }).join(" ");
  }
  const query = expressions.map((expression) => {
    if (expression.length === 1) {
      return generateExpression(expression);
    } else {
      return `(${generateExpression(expression)})`;
    }
  }).join(" ");
  return query;
}

This generator function takes an array of expressions as input and generates the filter query string.

For example, the following array of expressions:

[
  [
    { type: "field", field: "field1", operator: "equals", value: "value1" }
  ],
  [
    { type: "logical", operator: "AND" },
    { type: "field", field: "field2", operator: "equals", value: "value2" },
    { type: "logical", operator: "OR" },
    { type: "field", field: "field3", operator: "equals", value: "value3" }
  ]
]

will be generated into the following filter query string:

(field1: value1) AND (field2: value2 OR field3: value3)

Step 4: Create Transformation Functions

Finally, create transformation functions that can transform between the filter query string and the object representation.

Here are the transformation functions:

function queryToObject(queryString) {
  return parseFilterQuery(queryString);
}

function objectToQuery(object) {
  return generateFilterQuery(object);
}

These functions use the parser and generator functions created in Steps 2 and 3 to transform between the filter query string and the object representation.

Here’s an example usage:

const queryString = "(field1: value1) AND (field2: value2 OR field3: value3)";
const object = queryToObject(queryString);
console.log(object); // outputs the array of expressions
const newQueryString = objectToQuery(object);
console.log(newQueryString); // outputs the filter query string

Conclusion

In conclusion, building a filter query parser and generator in JavaScript can be a useful solution for a variety of applications, particularly when handling large datasets. By following the steps outlined in this article, developers can easily transform a filter query string into a more manageable object representation, perform complex queries, and generate filter query strings from objects. This type of solution is particularly useful for applications that need to handle complex filtering and sorting requirements, such as search engines, analytics platforms, and task management systems, like Jira. By leveraging the power of JavaScript, developers can build robust filter query solutions that meet the needs of their users and improve the performance and efficiency of their applications.

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