Resolve the JS-side corner case reported in [forum:7774b773937cbe0a | forum post 7774b773937cbe0a] by not caching oo1.Stmt.columnCount.

FossilOrigin-Name: c3d25c3a25e79e01c4ad0cf11f7dc3b0fb1932f3bcd04935a728ef62f7e07cf1

ext/wasm/api/sqlite3-api-oo1.js

@@ -330,10 +330,15 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
 
      - `db`: the DB object which created the statement.
 
-     - `columnCount`: the number of result columns in the query, or 0 for
+     - `columnCount`: the number of result columns in the query, or 0
-     queries which cannot return results.
+     for queries which cannot return results. This property is a proxy
+     for sqlite3_column_count() and its use in loops should be avoided
+     because of the call overhead associated with that. The
+     `columnCount` is not cached when the Stmt is created because a
+     schema change made via a separate db connection between this
+     statement's preparation and when it is stepped may invalidate it.
 
-     - `parameterCount`: the number of bindable paramters in the query.
+     - `parameterCount`: the number of bindable parameters in the query.
   */
   const Stmt = function(){
     if(BindTypes!==arguments[2]){
@@ -341,7 +346,6 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
     }
     this.db = arguments[0];
     __ptrMap.set(this, arguments[1]);
-    this.columnCount = capi.sqlite3_column_count(this.pointer);
     this.parameterCount = capi.sqlite3_bind_parameter_count(this.pointer);
   };
 
@@ -701,18 +705,18 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
        with identical names.
 
        - `callback` = a function which gets called for each row of the
-       result set, but only if that statement has any result
+       result set, but only if that statement has any result rows. The
-       _rows_. The callback's "this" is the options object, noting
+       callback's "this" is the options object, noting that this
-       that this function synthesizes one if the caller does not pass
+       function synthesizes one if the caller does not pass one to
-       one to exec(). The second argument passed to the callback is
+       exec(). The second argument passed to the callback is always
-       always the current Stmt object, as it's needed if the caller
+       the current Stmt object, as it's needed if the caller wants to
-       wants to fetch the column names or some such (noting that they
+       fetch the column names or some such (noting that they could
-       could also be fetched via `this.columnNames`, if the client
+       also be fetched via `this.columnNames`, if the client provides
-       provides the `columnNames` option). If the callback returns a
+       the `columnNames` option). If the callback returns a literal
-       literal `false` (as opposed to any other falsy value, e.g.  an
+       `false` (as opposed to any other falsy value, e.g. an implicit
-       implicit `undefined` return), any ongoing statement-`step()`
+       `undefined` return), any ongoing statement-`step()` iteration
-       iteration stops without an error. The return value of the
+       stops without an error. The return value of the callback is
-       callback is otherwise ignored.
+       otherwise ignored.
 
        ACHTUNG: The callback MUST NOT modify the Stmt object. Calling
        any of the Stmt.get() variants, Stmt.getColumnName(), or
@@ -733,7 +737,7 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
 
          A.1) `'array'` (the default) causes the results of
          `stmt.get([])` to be passed to the `callback` and/or appended
-         to `resultRows`
+         to `resultRows`.
 
          A.2) `'object'` causes the results of
          `stmt.get(Object.create(null))` to be passed to the
@@ -744,8 +748,8 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
 
          A.3) `'stmt'` causes the current Stmt to be passed to the
          callback, but this mode will trigger an exception if
-         `resultRows` is an array because appending the statement to
+         `resultRows` is an array because appending the transient
-         the array would be downright unhelpful.
+         statement to the array would be downright unhelpful.
 
        B) An integer, indicating a zero-based column in the result
        row. Only that one single value will be passed on.
@@ -857,14 +861,21 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
             bind = null;
           }
           if(evalFirstResult && stmt.columnCount){
-            /* Only forward SELECT results for the FIRST query
+            /* Only forward SELECT-style results for the FIRST query
                in the SQL which potentially has them. */
+            let gotColNames = Array.isArray(
+              opt.columnNames
+              /* As reported in
+                 https://sqlite.org/forum/forumpost/7774b773937cbe0a
+                 we need to delay fetching of the column names until
+                 after the first step() (if we step() at all) because
+                 a schema change between the prepare() and step(), via
+                 another connection, may invalidate the column count
+                 and names. */) ? 0 : 1;
             evalFirstResult = false;
-            if(Array.isArray(opt.columnNames)){
-              stmt.getColumnNames(opt.columnNames);
-            }
             if(arg.cbArg || resultRows){
               for(; stmt.step(); stmt._isLocked = false){
+                if(0===gotColNames++) stmt.getColumnNames(opt.columnNames);
                 stmt._isLocked = true;
                 const row = arg.cbArg(stmt);
                 if(resultRows) resultRows.push(row);
@@ -874,6 +885,10 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
               }
               stmt._isLocked = false;
             }
+            if(0===gotColNames){
+              /* opt.columnNames was provided but we visited no result rows */
+              stmt.getColumnNames(opt.columnNames);
+            }
           }else{
             stmt.step();
           }
@@ -1416,7 +1431,6 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
         capi.sqlite3_finalize(this.pointer);
         __ptrMap.delete(this);
         delete this._mayGet;
-        delete this.columnCount;
         delete this.parameterCount;
         delete this.db;
         delete this._isLocked;
@@ -1686,13 +1700,15 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
       }
       if(Array.isArray(ndx)){
         let i = 0;
-        while(i<this.columnCount){
+        const n = this.columnCount;
+        while(i<n){
           ndx[i] = this.get(i++);
         }
         return ndx;
       }else if(ndx && 'object'===typeof ndx){
         let i = 0;
-        while(i<this.columnCount){
+        const n = this.columnCount;
+        while(i<n){
           ndx[capi.sqlite3_column_name(this.pointer,i)] = this.get(i++);
         }
         return ndx;
@@ -1790,16 +1806,17 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
       );
     },
     /**
-       If this statement potentially has result columns, this
+       If this statement potentially has result columns, this function
-       function returns an array of all such names. If passed an
+       returns an array of all such names. If passed an array, it is
-       array, it is used as the target and all names are appended
+       used as the target and all names are appended to it. Returns
-       to it. Returns the target array. Throws if this statement
+       the target array. Throws if this statement cannot have result
-       cannot have result columns. This object's columnCount member
+       columns. This object's columnCount property holds the number of
-       holds the number of columns.
+       columns.
     */
     getColumnNames: function(tgt=[]){
       affirmColIndex(affirmStmtOpen(this),0);
-      for(let i = 0; i < this.columnCount; ++i){
+      const n = this.columnCount;
+      for(let i = 0; i < n; ++i){
         tgt.push(capi.sqlite3_column_name(this.pointer, i));
       }
       return tgt;
@@ -1826,6 +1843,21 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
     Object.defineProperty(Stmt.prototype, 'pointer', prop);
     Object.defineProperty(DB.prototype, 'pointer', prop);
   }
+  /**
+     A Stmt's columntCount property is an interceptor for
+     sqlite3_column_count().
+
+     This requires an unfortunate performance hit compared to caching
+     columnCount when the Stmt is created/prepared (as was done in
+     SQLite <=3.42.0), but is necessary in order to handle certain
+     corner cases, as described in
+     https://sqlite.org/forum/forumpost/7774b773937cbe0a.
+  */
+  Object.defineProperty(Stmt.prototype, 'columnCount', {
+    enumerable: false,
+    get: function(){return capi.sqlite3_column_count(this.pointer)},
+    set: ()=>toss3("The columnCount property is read-only.")
+  });
 
   /** The OO API's public namespace. */
   sqlite3.oo1 = {

ext/wasm/common/SqliteTestUtil.js

@@ -156,7 +156,6 @@
     }
   };
 
-  
   /**
      This is a module object for use with the emscripten-installed
      sqlite3InitModule() factory function.

ext/wasm/tester1.c-pp.js

@@ -1229,6 +1229,8 @@ self.sqlite3InitModule = sqlite3InitModule;
             ) === 0)
           .assert(!st._mayGet)
           .assert('a' === st.getColumnName(0))
+          .mustThrowMatching(()=>st.columnCount=2,
+                             /columnCount property is read-only/)
           .assert(1===st.columnCount)
           .assert(0===st.parameterCount)
           .mustThrow(()=>st.bind(1,null))
@@ -1373,10 +1375,10 @@ self.sqlite3InitModule = sqlite3InitModule;
           T.assert(
             3 === this._myState
             /* Recall that "this" is the options object. */
+          ).assert(
+            this.columnNames===colNames
           ).assert(
             this.columnNames[0]==='a' && this.columnNames[1]==='b'
-            /* options.columnNames is filled out before the first
-               Stmt.step(). */
           ).assert(
             (row.a%2 && row.a<6) || 'blob'===row.a
           );
@@ -1386,6 +1388,14 @@ self.sqlite3InitModule = sqlite3InitModule;
         .assert('a' === colNames[0])
         .assert(4 === counter)
         .assert(4 === list.length);
+      colNames = [];
+      db.exec({
+        /* Ensure that columnNames is populated for empty result sets. */
+        sql: "SELECT a a, b B FROM t WHERE 0",
+        columnNames: colNames
+      });
+      T.assert(2===colNames.length)
+        .assert('a'===colNames[0] && 'B'===colNames[1]);
       list.length = 0;
       db.exec("SELECT a a, b b FROM t",{
         rowMode: 'array',
@@ -1438,6 +1448,7 @@ self.sqlite3InitModule = sqlite3InitModule;
 
       let st = db.prepare("update t set b=:b where a='blob'");
       try {
+        T.assert(0===st.columnCount);
         const ndx = st.getParamIndex(':b');
         T.assert(1===ndx);
         st.bindAsBlob(ndx, "ima blob").reset(true);

manifest

@@ -1,5 +1,5 @@
-C Enhance\sthe\ssplit-sqlite3c.tcl\sscript\sso\sthat\sit\suses\ssingle-character\nextensions\son\ssubordinate\ssource\sfiles,\seven\swhen\sthe\snumber\sof\ssubordinates\nexceeds\s9.\s\sThis\sis\snot\syet\sneeded,\sbut\smight\sbe\ssoon.
+C Resolve\sthe\sJS-side\scorner\scase\sreported\sin\s[forum:7774b773937cbe0a\s|\sforum\spost\s7774b773937cbe0a]\sby\snot\scaching\soo1.Stmt.columnCount.
-D 2023-05-10T16:04:04.601
+D 2023-05-10T21:06:02.101
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
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 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -493,7 +493,7 @@ F ext/wasm/api/post-js-header.js 47b6b281f39ad59fa6e8b658308cd98ea292c286a68407b
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 F ext/wasm/batch-runner.html 4deeed44fe41496dc6898d9fb17938ea3291f40f4bfb977e29d0cef96fbbe4c8
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-F ext/wasm/common/SqliteTestUtil.js d8bf97ecb0705a2299765c8fc9e11b1a5ac7f10988bbf375a6558b7ca287067b
+F ext/wasm/common/SqliteTestUtil.js 7adaeffef757d8708418dc9190f72df22367b531831775804b31598b44f6aa51
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@@ -545,7 +545,7 @@ F ext/wasm/test-opfs-vfs.html 1f2d672f3f3fce810dfd48a8d56914aba22e45c6834e262555
 F ext/wasm/test-opfs-vfs.js f09266873e1a34d9bdb6d3981ec8c9e382f31f215c9fd2f9016d2394b8ae9b7b
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-F ext/wasm/tester1.c-pp.js 587a18db0f794c594eb0fade37c92af3e2370501576bb08dafd8ed7d009b6516
+F ext/wasm/tester1.c-pp.js 2682abac377af9625f23837b7cfdbd0d8e0d5fee4d2acf3c98e1564785ccc479
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@@ -2068,8 +2068,11 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
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-R 7825f403dc8e20a9b2cba11eaedce32c
+R 4aa19a03c6b96f49d09013b0f165e4f7
-U drh
+T *branch * oo1-no-cache-Stmt.columnCount
-Z 0780e89a4d80820b94f58c1bb18accfa
+T *sym-oo1-no-cache-Stmt.columnCount *
+T -sym-trunk * Cancelled\sby\sbranch.
+U stephan
+Z a06e6de30a703955eb7f478e54c3db62
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
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+c3d25c3a25e79e01c4ad0cf11f7dc3b0fb1932f3bcd04935a728ef62f7e07cf1