diff --git a/ql/src/codeql_ql/ast/Ast.qll b/ql/src/codeql_ql/ast/Ast.qll
index 0cc407e4d68..ea5b4c00753 100644
--- a/ql/src/codeql_ql/ast/Ast.qll
+++ b/ql/src/codeql_ql/ast/Ast.qll
@@ -4,6 +4,14 @@ private import codeql_ql.ast.internal.Module
 private import codeql_ql.ast.internal.Predicate
 private import codeql_ql.ast.internal.Type
 
+bindingset[name, i]
+private string indexedMember(string name, int i) { result = name + "(" + i.toString() + ")" }
+
+bindingset[name, index]
+private string stringIndexedMember(string name, string index) {
+  result = name + "(\"" + index + "\")"
+}
+
 /** An AST node of a QL program */
 class AstNode extends TAstNode {
   string toString() { result = getAPrimaryQlClass() }
@@ -20,6 +28,13 @@ class AstNode extends TAstNode {
     not result = this
   }
 
+  /**
+   * Gets a child of this node, which can also be retrieved using a predicate
+   * named `pred`.
+   */
+  cached
+  AstNode getAChild(string pred) { none() }
+
   string getAPrimaryQlClass() { result = "???" }
 }
 
@@ -30,6 +45,10 @@ class TopLevel extends TTopLevel, AstNode {
 
   ModuleMember getAMember() { toGenerated(result) = file.getChild(_).getChild(_) }
 
+  override ModuleMember getAChild(string pred) {
+    pred = "getAMember" and result = this.getAMember()
+  }
+
   override string getAPrimaryQlClass() { result = "TopLevel" }
 }
 
@@ -51,6 +70,18 @@ class Select extends TSelect, AstNode {
     toGenerated(result) = sel.getChild(_).(Generated::OrderBys).getChild(i).getChild(0)
   }
 
+  override AstNode getAChild(string pred) {
+    pred = "getWhere" and result = this.getWhere()
+    or
+    exists(int i |
+      pred = indexedMember("getVarDecl", i) and result = this.getVarDecl(i)
+      or
+      pred = indexedMember("getAsExpr", i) and result = this.getAsExpr(i)
+      or
+      pred = indexedMember("getOrderBy", i) and result = this.getOrderBy(i)
+    )
+  }
+
   override string getAPrimaryQlClass() { result = "Select" }
   // TODO: Getters for VarDecls, Where-clause, selects.
 }
@@ -73,7 +104,15 @@ class Predicate extends TPredicate, AstNode {
    * Gets the `i`th parameter of the predicate.
    */
   VarDecl getParameter(int i) { none() }
+
   // TODO: ReturnType.
+  override AstNode getAChild(string pred) {
+    pred = "getBody" and result = this.getBody()
+    or
+    exists(int i | pred = indexedMember("getParameter", i) and result = this.getParameter(i))
+  }
+
+  override string getAPrimaryQlClass() { result = "Predicate" }
 }
 
 class PredicateExpr extends TPredicateExpr, AstNode {
@@ -111,6 +150,8 @@ class PredicateExpr extends TPredicateExpr, AstNode {
     this in [result.(ClasslessPredicate).getAlias(), result.(HigherOrderFormula).getInput(_)]
   }
 
+  override AstNode getAChild(string pred) { pred = "getQualifier" and result = this.getQualifier() }
+
   override string getAPrimaryQlClass() { result = "PredicateExpr" }
 }
 
@@ -144,6 +185,14 @@ class ClasslessPredicate extends TClasslessPredicate, Predicate, ModuleDeclarati
     toGenerated(result) =
       rank[i](Generated::VarDecl decl, int index | decl = pred.getChild(index) | decl order by index)
   }
+
+  override AstNode getAChild(string pred_name) {
+    pred_name = "getAlias" and result = this.getAlias()
+    or
+    pred_name = "getBody" and result = this.getBody()
+    or
+    exists(int i | pred_name = indexedMember("getParameter", i) and result = this.getParameter(i))
+  }
 }
 
 /**
@@ -166,6 +215,12 @@ class ClassPredicate extends TClassPredicate, Predicate {
     toGenerated(result) =
       rank[i](Generated::VarDecl decl, int index | decl = pred.getChild(index) | decl order by index)
   }
+
+  override AstNode getAChild(string pred_name) {
+    pred_name = "getBody" and result = this.getBody()
+    or
+    exists(int i | pred_name = indexedMember("getParameter", i) and result = this.getParameter(i))
+  }
 }
 
 /**
@@ -183,6 +238,8 @@ class CharPred extends TCharPred, Predicate {
   override string getName() { result = getParent().getName() }
 
   override Class getParent() { result.getCharPred() = this }
+
+  override AstNode getAChild(string pred_name) { pred_name = "getBody" and result = this.getBody() }
 }
 
 /**
@@ -211,6 +268,8 @@ class VarDecl extends TVarDecl, AstNode {
   }
 
   TypeExpr getType() { toGenerated(result) = var.getChild(0) }
+
+  override AstNode getAChild(string pred) { pred = "getType" and result = this.getType() }
 }
 
 /**
@@ -298,6 +357,12 @@ class Module extends TModule, ModuleDeclaration {
   ModuleExpr getAlias() {
     toGenerated(result) = mod.getAFieldOrChild().(Generated::ModuleAliasBody).getChild()
   }
+
+  override AstNode getAChild(string pred) {
+    pred = "getAlias" and result = this.getAlias()
+    or
+    pred = "getAMember" and result = this.getAMember()
+  }
 }
 
 /**
@@ -384,6 +449,23 @@ class Class extends TClass, TypeDeclaration, ModuleDeclaration {
   TypeExpr getUnionMember() {
     toGenerated(result) = cls.getChild(_).(Generated::TypeUnionBody).getChild(_)
   }
+
+  override AstNode getAChild(string pred) {
+    pred = "getAliasType" and result = this.getAliasType()
+    or
+    pred = "getUnionMember" and result = this.getUnionMember()
+    or
+    pred = "getAField" and result = this.getAField()
+    or
+    pred = "getCharPred" and result = this.getCharPred()
+    or
+    pred = "getASuperType" and result = this.getASuperType()
+    or
+    exists(string name |
+      pred = stringIndexedMember("getClassPredicate", name) and
+      result = this.getClassPredicate(name)
+    )
+  }
 }
 
 /**
@@ -409,6 +491,8 @@ class NewType extends TNewType, TypeDeclaration, ModuleDeclaration {
    * Gets a branch in this `newtype`.
    */
   NewTypeBranch getABranch() { toGenerated(result) = type.getChild().getChild(_) }
+
+  override AstNode getAChild(string pred) { pred = "getABranch" and result = this.getABranch() }
 }
 
 /**
@@ -433,6 +517,12 @@ class NewTypeBranch extends TNewTypeBranch, TypeDeclaration {
   Formula getBody() { toGenerated(result) = branch.getChild(_).(Generated::Body).getChild() }
 
   override NewType getParent() { result.getABranch() = this }
+
+  override AstNode getAChild(string pred) {
+    pred = "getBody" and result = this.getBody()
+    or
+    exists(int i | pred = indexedMember("getField", i) and result = this.getField(i))
+  }
 }
 
 class Call extends TCall, AstNode {
@@ -466,6 +556,12 @@ class PredicateCall extends TPredicateCall, Call {
   string getPredicateName() {
     result = expr.getChild(0).(Generated::AritylessPredicateExpr).getName().getValue()
   }
+
+  override AstNode getAChild(string pred) {
+    exists(int i | pred = indexedMember("getArgument", i) and result = this.getArgument(i))
+    or
+    pred = "getQualifier" and result = this.getQualifier()
+  }
 }
 
 class MemberCall extends TMemberCall, Call {
@@ -498,6 +594,14 @@ class MemberCall extends TMemberCall, Call {
   }
 
   Expr getBase() { toGenerated(result) = expr.getChild(0) }
+
+  override AstNode getAChild(string pred) {
+    pred = "getBase" and result = this.getBase()
+    or
+    pred = "getSuperType" and result = this.getSuperType()
+    or
+    exists(int i | pred = indexedMember("getArgument", i) and result = this.getArgument(i))
+  }
 }
 
 class NoneCall extends TNoneCall, Call, Formula {
@@ -528,6 +632,12 @@ class InlineCast extends TInlineCast, Expr {
   }
 
   Expr getBase() { toGenerated(result) = expr.getChild(0) }
+
+  override AstNode getAChild(string pred) {
+    pred = "getType" and result = this.getType()
+    or
+    pred = "getBase" and result = this.getBase()
+  }
 }
 
 /** An entity that resolves to a module. */
@@ -608,6 +718,8 @@ class Conjunction extends TConjunction, AstNode, Formula {
 
   /** Gets an operand to this formula. */
   Formula getAnOperand() { toGenerated(result) in [conj.getLeft(), conj.getRight()] }
+
+  override AstNode getAChild(string pred) { pred = "getAnOperand" and result = this.getAnOperand() }
 }
 
 /** An `or` formula, with 2 or more operands. */
@@ -620,6 +732,8 @@ class Disjunction extends TDisjunction, AstNode {
 
   /** Gets an operand to this formula. */
   Formula getAnOperand() { toGenerated(result) in [disj.getLeft(), disj.getRight()] }
+
+  override AstNode getAChild(string pred) { pred = "getAnOperand" and result = this.getAnOperand() }
 }
 
 /**
@@ -700,6 +814,12 @@ class ComparisonFormula extends TComparisonFormula, Formula {
   ComparisonSymbol getSymbol() { result = this.getOperator().getSymbol() }
 
   override string getAPrimaryQlClass() { result = "ComparisonFormula" }
+
+  override AstNode getAChild(string pred) {
+    pred = "getLeftOperand" and result = this.getLeftOperand()
+    or
+    pred = "getRightOperand" and result = this.getRightOperand()
+  }
 }
 
 /** A quantifier formula, such as `exists` or `forall`. */
@@ -742,6 +862,16 @@ class Quantifier extends TQuantifier, Formula {
   predicate hasExpr() { exists(getExpr()) }
 
   override string getAPrimaryQlClass() { result = "Quantifier" }
+
+  override AstNode getAChild(string pred) {
+    exists(int i | pred = indexedMember("getArgument", i) and result = this.getArgument(i))
+    or
+    pred = "getRange" and result = this.getRange()
+    or
+    pred = "getFormula" and result = this.getFormula()
+    or
+    pred = "getExpr" and result = this.getExpr()
+  }
 }
 
 /** An `exists` quantifier. */
@@ -781,6 +911,14 @@ class IfFormula extends TIfFormula, Formula {
   Formula getElsePart() { toGenerated(result) = ifterm.getSecond() }
 
   override string getAPrimaryQlClass() { result = "IfFormula" }
+
+  override AstNode getAChild(string pred) {
+    pred = "getCondition" and result = this.getCondition()
+    or
+    pred = "getThenPart" and result = this.getThenPart()
+    or
+    pred = "getElsePart" and result = this.getElsePart()
+  }
 }
 
 /**
@@ -798,6 +936,12 @@ class Implication extends TImplication, Formula {
   Formula getRightOperand() { toGenerated(result) = imp.getRight() }
 
   override string getAPrimaryQlClass() { result = "Implication" }
+
+  override AstNode getAChild(string pred) {
+    pred = "getLeftOperand" and result = this.getLeftOperand()
+    or
+    pred = "getRightOperand" and result = this.getRightOperand()
+  }
 }
 
 /**
@@ -817,6 +961,12 @@ class InstanceOf extends TInstanceOf, Formula {
   /** Gets the type being checked. */
   //QLTypeExpr getType() { result = getTypeRef().getType() }
   override string getAPrimaryQlClass() { result = "InstanceOf" }
+
+  override AstNode getAChild(string pred) {
+    pred = "getExpr" and result = this.getExpr()
+    or
+    pred = "getType" and result = this.getType()
+  }
 }
 
 class InFormula extends TInFormula, Formula {
@@ -829,6 +979,12 @@ class InFormula extends TInFormula, Formula {
   Expr getRange() { toGenerated(result) = inexpr.getRight() }
 
   override string getAPrimaryQlClass() { result = "InFormula" }
+
+  override AstNode getAChild(string pred) {
+    pred = "getExpr" and result = this.getExpr()
+    or
+    pred = "getRange" and result = this.getRange()
+  }
 }
 
 class HigherOrderFormula extends THigherOrderFormula, Formula {
@@ -845,6 +1001,14 @@ class HigherOrderFormula extends THigherOrderFormula, Formula {
   string getName() { result = hop.getName().getValue() }
 
   override string getAPrimaryQlClass() { result = "HigherOrderFormula" }
+
+  override AstNode getAChild(string pred) {
+    exists(int i |
+      pred = indexedMember("getInput", i) and result = this.getInput(i)
+      or
+      pred = indexedMember("getArgument", i) and result = this.getArgument(i)
+    )
+  }
 }
 
 class ExprAggregate extends TExprAggregate, Expr {
@@ -878,6 +1042,14 @@ class ExprAggregate extends TExprAggregate, Expr {
   }
 
   override string getAPrimaryQlClass() { result = "ExprAggregate[" + kind + "]" }
+
+  override AstNode getAChild(string pred) {
+    exists(int i |
+      pred = indexedMember("getAsExpr", i) and result = this.getAsExpr(i)
+      or
+      pred = indexedMember("getOrderBy", i) and result = this.getOrderBy(i)
+    )
+  }
 }
 
 /** An aggregate expression, such as `count` or `sum`. */
@@ -923,6 +1095,16 @@ class Aggregate extends TAggregate, Expr {
   }
 
   override string getAPrimaryQlClass() { result = "Aggregate[" + kind + "]" }
+
+  override AstNode getAChild(string pred) {
+    exists(int i |
+      pred = indexedMember("getArgument", i) and result = this.getArgument(i)
+      or
+      pred = indexedMember("getAsExpr", i) and result = this.getAsExpr(i)
+      or
+      pred = indexedMember("getOrderBy", i) and result = this.getOrderBy(i)
+    )
+  }
 }
 
 /**
@@ -937,6 +1119,8 @@ class Rank extends Aggregate {
    * The `i` in `rank[i]( | | )`.
    */
   Expr getRankExpr() { toGenerated(result) = agg.getChild(1) }
+
+  override AstNode getAChild(string pred) { pred = "getRankExpr" and result = this.getRankExpr() }
 }
 
 /**
@@ -970,6 +1154,8 @@ class AsExpr extends TAsExpr, AstNode {
     or
     result.(Select).getAsExpr(_) = this
   }
+
+  override AstNode getAChild(string pred) { pred = "getInnerExpr" and result = this.getInnerExpr() }
 }
 
 class Identifier extends TIdentifier, Expr {
@@ -992,6 +1178,8 @@ class Negation extends TNegation, Formula {
   Formula getFormula() { toGenerated(result) = neg.getChild() }
 
   override string getAPrimaryQlClass() { result = "Negation" }
+
+  override AstNode getAChild(string pred) { pred = "getFormula" and result = this.getFormula() }
 }
 
 /** An expression, such as `x+4`. */
@@ -1021,6 +1209,10 @@ class ExprAnnotation extends TExprAnnotation, Expr {
   Expr getExpression() { toGenerated(result) = expr_anno.getChild() }
 
   override string getAPrimaryQlClass() { result = "ExprAnnotation" }
+
+  override AstNode getAChild(string pred) {
+    pred = "getExpression" and result = this.getExpression()
+  }
 }
 
 /** A function symbol, such as `+` or `*`. */
@@ -1053,6 +1245,12 @@ class AddSubExpr extends TAddSubExpr, BinOpExpr {
 
   /** Gets the operator of the binary expression. */
   FunctionSymbol getOperator() { result = operator }
+
+  override AstNode getAChild(string pred) {
+    pred = "getLeftOperand" and result = this.getLeftOperand()
+    or
+    pred = "getRightOperand" and result = this.getRightOperand()
+  }
 }
 
 /**
@@ -1093,6 +1291,12 @@ class MulDivModExpr extends TMulDivModExpr, BinOpExpr {
 
   /** Gets the operator of the binary expression. */
   FunctionSymbol getOperator() { result = operator }
+
+  override AstNode getAChild(string pred) {
+    pred = "getLeftOperand" and result = this.getLeftOperand()
+    or
+    pred = "getRightOperand" and result = this.getRightOperand()
+  }
 }
 
 /**
@@ -1141,6 +1345,12 @@ class Range extends TRange, Expr {
   Expr getHighEndpoint() { toGenerated(result) = range.getUpper() }
 
   override string getAPrimaryQlClass() { result = "Range" }
+
+  override AstNode getAChild(string pred) {
+    pred = "getLowEndpoint" and result = this.getLowEndpoint()
+    or
+    pred = "getHighEndpoint" and result = this.getHighEndpoint()
+  }
 }
 
 /**
@@ -1157,6 +1367,10 @@ class Set extends TSet, Expr {
   Expr getElement(int i) { toGenerated(result) = set.getChild(i) }
 
   override string getAPrimaryQlClass() { result = "Set" }
+
+  override AstNode getAChild(string pred) {
+    exists(int i | pred = indexedMember("getElement", i) and result = getElement(i))
+  }
 }
 
 /** A unary operation expression, such as `-(x*y)` */
@@ -1170,6 +1384,10 @@ class UnaryExpr extends TUnaryExpr, Expr {
 
   /** Gets the operator of the unary expression as a string. */
   FunctionSymbol getOperator() { result = unaryexpr.getChild(0).toString() }
+
+  override string getAPrimaryQlClass() { result = "UnaryExpr" }
+
+  override AstNode getAChild(string pred) { pred = "getOperand" and result = this.getOperand() }
 }
 
 /** A "don't care" expression, denoted by `_`. */
@@ -1221,10 +1439,10 @@ class ModuleExpr extends TModuleExpr, ModuleRef {
 
   override AstNode getParent() {
     result = super.getParent() or
-    result.(PredicateCall).getQualifier() = this
-    or
-    result.(PredicateExpr).getQualifier() = this
-    or
+    result.(PredicateCall).getQualifier() = this or
+    result.(PredicateExpr).getQualifier() = this or
     result.(Module).getAlias() = this
   }
+
+  override AstNode getAChild(string pred) { pred = "getQualifier" and result = this.getQualifier() }
 }