CouchDB设计文档保存失败：表达式无法解析为函数及修复问询

Let's break down what's going wrong with your design document and fix it step by step. The error "Expression does not eval to a function" and failed document creation stem from several key misunderstandings about how CouchDB's validate_doc_update works, plus syntax and logic errors in your code.

Key Issues in Your Current Code #

1. Wrong Return Pattern for validate_doc_update #

CouchDB's validate_doc_update function doesn't return arrays like [doc, "message"]—that's a pattern for other CouchDB handlers (like update functions). Instead:

• If the update is allowed, you don't return anything (or return undefined).
• If it's not allowed, you throw an error with throw new Error("Your error message").

Your current code returns arrays, which is why CouchDB complains it can't evaluate to a valid function.

2. Using Invalid Variables & Functions #

• req: This variable doesn't exist in the validate_doc_update context—your parameters are newDoc, oldDoc, userCtx, secObj.
• doc: You reference doc but your incoming document is newDoc (for creates/updates) or oldDoc (for existing docs).
• emit(): This is only used in view map functions, not in validation functions.
• HTML-escaped characters: && should be &&, < should be <, + = should be +=—these syntax errors break the function.

3. Mixing Validation & Business Logic #

You're trying to calculate the average of points and update the document inside the validation function, but validate_doc_update is only meant to check permissions and document validity—it shouldn't modify documents or run aggregation logic. That logic belongs in an update handler or a separate process that uses CouchDB views to compute averages.

Fixed Design Document #

First, let's fix the validate_doc_update function to handle only permission checks correctly, then add the aggregation logic in the right place:

{
  "_id": "_design/marea",
  "language": "javascript",
  "validate_doc_update": "function(newDoc, oldDoc, userCtx, secObj) {
    // Allow users with '2018marea' role OR the original document owner to make changes
    const hasPermission = userCtx.roles.indexOf('2018marea') !== -1 || (oldDoc && userCtx.name === oldDoc.name);
    
    if (!hasPermission) {
      throw new Error('Cannot Overwrite Data: You do not have permission to modify this document');
    }

    // Optional: Add check to ensure 'points' field exists for new documents
    if (!oldDoc && newDoc.points === undefined) {
      throw new Error('New document must include a "points" field');
    }
  }",
  // Update handler to calculate and save team points average
  "updates": {
    "update_team_average": "function(doc, req) {
      if (!doc) {
        return [null, 'Empty Database: No document found to update'];
      }

      // Fetch all documents for the current doc's team using our view
      const teamViewResults = req.query.view('/_design/marea/_view/by_team', { key: doc.team });
      const pointsArray = teamViewResults.rows
        .map(row => row.value.points)
        .filter(point => typeof point === 'number');

      // Calculate average
      const totalPoints = pointsArray.reduce((sum, point) => sum + point, 0);
      doc.team_points_average = pointsArray.length > 0 ? totalPoints / pointsArray.length : 0;
      doc.edited_by = req.userCtx.name;

      return [doc, 'Successfully updated team points average'];
    }"
  },
  // View to fetch documents grouped by team
  "views": {
    "by_team": {
      "map": "function(doc) {
        if (doc.team && typeof doc.points === 'number') {
          emit(doc.team, { points: doc.points });
        }
      }"
    }
  }
}

How This Works #

1. Validated Permissions: The validate_doc_update now properly checks if the user has the 2018marea role or is the document owner. If not, it throws a clear error. It also optionally enforces that new documents include a points field.

2. Team Average Calculation:

   • The by_team view maps documents by their team field, emitting the team as the key and the points value.
   • The update_team_average update handler uses this view to fetch all documents for the current doc's team, calculates the average, and updates the document with the result and editor's name.

3. Correct Syntax: All escaped characters are fixed, and we're using valid variables for each context (e.g., req is available in update handlers, not validation).

Usage Notes #

• To create a document: Users with the 2018marea role can POST to the database normally, as long as the document includes points (if you kept that check).
• To update the team average: Call the update handler with a request like POST /your-database/_design/marea/_update/update_team_average/{target-document-id}.

内容的提问来源于stack exchange，提问作者ShashJar