csharp-sdk-upm/Storage/Source/Public/AVQueryExtensions.cs

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2019-07-19 15:01:34 +08:00
using LeanCloud.Storage.Internal;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
namespace LeanCloud
{
/// <summary>
/// Provides extension methods for <see cref="AVQuery{T}"/> to support
/// Linq-style queries.
/// </summary>
public static class AVQueryExtensions
{
private static readonly MethodInfo getMethod;
private static readonly MethodInfo stringContains;
private static readonly MethodInfo stringStartsWith;
private static readonly MethodInfo stringEndsWith;
private static readonly MethodInfo containsMethod;
private static readonly MethodInfo notContainsMethod;
private static readonly MethodInfo containsKeyMethod;
private static readonly MethodInfo notContainsKeyMethod;
private static readonly Dictionary<MethodInfo, MethodInfo> functionMappings;
static AVQueryExtensions()
{
getMethod = GetMethod<AVObject>(obj => obj.Get<int>(null)).GetGenericMethodDefinition();
stringContains = GetMethod<string>(str => str.Contains(null));
stringStartsWith = GetMethod<string>(str => str.StartsWith(null));
stringEndsWith = GetMethod<string>(str => str.EndsWith(null));
functionMappings = new Dictionary<MethodInfo, MethodInfo> {
{
stringContains,
GetMethod<AVQuery<AVObject>>(q => q.WhereContains(null, null))
},
{
stringStartsWith,
GetMethod<AVQuery<AVObject>>(q => q.WhereStartsWith(null, null))
},
{
stringEndsWith,
GetMethod<AVQuery<AVObject>>(q => q.WhereEndsWith(null,null))
},
};
containsMethod = GetMethod<object>(
o => AVQueryExtensions.ContainsStub<object>(null, null)).GetGenericMethodDefinition();
notContainsMethod = GetMethod<object>(
o => AVQueryExtensions.NotContainsStub<object>(null, null))
.GetGenericMethodDefinition();
containsKeyMethod = GetMethod<object>(o => AVQueryExtensions.ContainsKeyStub(null, null));
notContainsKeyMethod = GetMethod<object>(
o => AVQueryExtensions.NotContainsKeyStub(null, null));
}
/// <summary>
/// Gets a MethodInfo for a top-level method call.
/// </summary>
private static MethodInfo GetMethod<T>(Expression<Action<T>> expression)
{
return (expression.Body as MethodCallExpression).Method;
}
/// <summary>
/// When a query is normalized, this is a placeholder to indicate we should
/// add a WhereContainedIn() clause.
/// </summary>
private static bool ContainsStub<T>(object collection, T value)
{
throw new NotImplementedException(
"Exists only for expression translation as a placeholder.");
}
/// <summary>
/// When a query is normalized, this is a placeholder to indicate we should
/// add a WhereNotContainedIn() clause.
/// </summary>
private static bool NotContainsStub<T>(object collection, T value)
{
throw new NotImplementedException(
"Exists only for expression translation as a placeholder.");
}
/// <summary>
/// When a query is normalized, this is a placeholder to indicate that we should
/// add a WhereExists() clause.
/// </summary>
private static bool ContainsKeyStub(AVObject obj, string key)
{
throw new NotImplementedException(
"Exists only for expression translation as a placeholder.");
}
/// <summary>
/// When a query is normalized, this is a placeholder to indicate that we should
/// add a WhereDoesNotExist() clause.
/// </summary>
private static bool NotContainsKeyStub(AVObject obj, string key)
{
throw new NotImplementedException(
"Exists only for expression translation as a placeholder.");
}
/// <summary>
/// Evaluates an expression and throws if the expression has components that can't be
/// evaluated (e.g. uses the parameter that's only represented by an object on the server).
/// </summary>
private static object GetValue(Expression exp)
{
try
{
return Expression.Lambda(
typeof(Func<>).MakeGenericType(exp.Type), exp).Compile().DynamicInvoke();
}
catch (Exception e)
{
throw new InvalidOperationException("Unable to evaluate expression: " + exp, e);
}
}
/// <summary>
/// Checks whether the MethodCallExpression is a call to AVObject.Get(),
/// which is the call we normalize all indexing into the AVObject to.
/// </summary>
private static bool IsAVObjectGet(MethodCallExpression node)
{
if (node == null || node.Object == null)
{
return false;
}
if (!typeof(AVObject).GetTypeInfo().IsAssignableFrom(node.Object.Type.GetTypeInfo()))
{
return false;
}
return node.Method.IsGenericMethod && node.Method.GetGenericMethodDefinition() == getMethod;
}
/// <summary>
/// Visits an Expression, converting AVObject.Get/AVObject[]/AVObject.Property,
/// and nested indices into a single call to AVObject.Get() with a "field path" like
/// "foo.bar.baz"
/// </summary>
private class ObjectNormalizer : ExpressionVisitor
{
protected override Expression VisitIndex(IndexExpression node)
{
var visitedObject = Visit(node.Object);
var indexer = visitedObject as MethodCallExpression;
if (IsAVObjectGet(indexer))
{
var indexValue = GetValue(node.Arguments[0]) as string;
if (indexValue == null)
{
throw new InvalidOperationException("Index must be a string");
}
var newPath = GetValue(indexer.Arguments[0]) + "." + indexValue;
return Expression.Call(indexer.Object,
getMethod.MakeGenericMethod(node.Type),
Expression.Constant(newPath, typeof(string)));
}
return base.VisitIndex(node);
}
/// <summary>
/// Check for a AVFieldName attribute and use that as the path component, turning
/// properties like foo.ObjectId into foo.Get("objectId")
/// </summary>
protected override Expression VisitMember(MemberExpression node)
{
var fieldName = node.Member.GetCustomAttribute<AVFieldNameAttribute>();
if (fieldName != null &&
typeof(AVObject).GetTypeInfo().IsAssignableFrom(node.Expression.Type.GetTypeInfo()))
{
var newPath = fieldName.FieldName;
return Expression.Call(node.Expression,
getMethod.MakeGenericMethod(node.Type),
Expression.Constant(newPath, typeof(string)));
}
return base.VisitMember(node);
}
/// <summary>
/// If a AVObject.Get() call has been cast, just change the generic parameter.
/// </summary>
protected override Expression VisitUnary(UnaryExpression node)
{
var methodCall = Visit(node.Operand) as MethodCallExpression;
if ((node.NodeType == ExpressionType.Convert ||
node.NodeType == ExpressionType.ConvertChecked) &&
IsAVObjectGet(methodCall))
{
return Expression.Call(methodCall.Object,
getMethod.MakeGenericMethod(node.Type),
methodCall.Arguments);
}
return base.VisitUnary(node);
}
protected override Expression VisitMethodCall(MethodCallExpression node)
{
if (node.Method.Name == "get_Item" && node.Object is ParameterExpression)
{
var indexPath = GetValue(node.Arguments[0]) as string;
return Expression.Call(node.Object,
getMethod.MakeGenericMethod(typeof(object)),
Expression.Constant(indexPath, typeof(string)));
}
if (node.Method.Name == "get_Item" || IsAVObjectGet(node))
{
var visitedObject = Visit(node.Object);
var indexer = visitedObject as MethodCallExpression;
if (IsAVObjectGet(indexer))
{
var indexValue = GetValue(node.Arguments[0]) as string;
if (indexValue == null)
{
throw new InvalidOperationException("Index must be a string");
}
var newPath = GetValue(indexer.Arguments[0]) + "." + indexValue;
return Expression.Call(indexer.Object,
getMethod.MakeGenericMethod(node.Type),
Expression.Constant(newPath, typeof(string)));
}
}
return base.VisitMethodCall(node);
}
}
/// <summary>
/// Normalizes Where expressions.
/// </summary>
private class WhereNormalizer : ExpressionVisitor
{
/// <summary>
/// Normalizes binary operators. &lt;, &gt;, &lt;=, &gt;= !=, and ==
/// This puts the AVObject.Get() on the left side of the operation
/// (reversing it if necessary), and normalizes the AVObject.Get()
/// </summary>
protected override Expression VisitBinary(BinaryExpression node)
{
var leftTransformed = new ObjectNormalizer().Visit(node.Left) as MethodCallExpression;
var rightTransformed = new ObjectNormalizer().Visit(node.Right) as MethodCallExpression;
MethodCallExpression objectExpression;
Expression filterExpression;
bool inverted;
if (leftTransformed != null)
{
objectExpression = leftTransformed;
filterExpression = node.Right;
inverted = false;
}
else
{
objectExpression = rightTransformed;
filterExpression = node.Left;
inverted = true;
}
try
{
switch (node.NodeType)
{
case ExpressionType.GreaterThan:
if (inverted)
{
return Expression.LessThan(objectExpression, filterExpression);
}
else
{
return Expression.GreaterThan(objectExpression, filterExpression);
}
case ExpressionType.GreaterThanOrEqual:
if (inverted)
{
return Expression.LessThanOrEqual(objectExpression, filterExpression);
}
else
{
return Expression.GreaterThanOrEqual(objectExpression, filterExpression);
}
case ExpressionType.LessThan:
if (inverted)
{
return Expression.GreaterThan(objectExpression, filterExpression);
}
else
{
return Expression.LessThan(objectExpression, filterExpression);
}
case ExpressionType.LessThanOrEqual:
if (inverted)
{
return Expression.GreaterThanOrEqual(objectExpression, filterExpression);
}
else
{
return Expression.LessThanOrEqual(objectExpression, filterExpression);
}
case ExpressionType.Equal:
return Expression.Equal(objectExpression, filterExpression);
case ExpressionType.NotEqual:
return Expression.NotEqual(objectExpression, filterExpression);
}
}
catch (ArgumentException)
{
throw new InvalidOperationException("Operation not supported: " + node);
}
return base.VisitBinary(node);
}
/// <summary>
/// If a ! operator is used, this removes the ! and instead calls the equivalent
/// function (so e.g. == becomes !=, &lt; becomes &gt;=, Contains becomes NotContains)
/// </summary>
protected override Expression VisitUnary(UnaryExpression node)
{
// Normalizes inversion
if (node.NodeType == ExpressionType.Not)
{
var visitedOperand = Visit(node.Operand);
var binaryOperand = visitedOperand as BinaryExpression;
if (binaryOperand != null)
{
switch (binaryOperand.NodeType)
{
case ExpressionType.GreaterThan:
return Expression.LessThanOrEqual(binaryOperand.Left, binaryOperand.Right);
case ExpressionType.GreaterThanOrEqual:
return Expression.LessThan(binaryOperand.Left, binaryOperand.Right);
case ExpressionType.LessThan:
return Expression.GreaterThanOrEqual(binaryOperand.Left, binaryOperand.Right);
case ExpressionType.LessThanOrEqual:
return Expression.GreaterThan(binaryOperand.Left, binaryOperand.Right);
case ExpressionType.Equal:
return Expression.NotEqual(binaryOperand.Left, binaryOperand.Right);
case ExpressionType.NotEqual:
return Expression.Equal(binaryOperand.Left, binaryOperand.Right);
}
}
var methodCallOperand = visitedOperand as MethodCallExpression;
if (methodCallOperand != null)
{
if (methodCallOperand.Method.IsGenericMethod)
{
if (methodCallOperand.Method.GetGenericMethodDefinition() == containsMethod)
{
var genericNotContains = notContainsMethod.MakeGenericMethod(
methodCallOperand.Method.GetGenericArguments());
return Expression.Call(genericNotContains, methodCallOperand.Arguments.ToArray());
}
if (methodCallOperand.Method.GetGenericMethodDefinition() == notContainsMethod)
{
var genericContains = containsMethod.MakeGenericMethod(
methodCallOperand.Method.GetGenericArguments());
return Expression.Call(genericContains, methodCallOperand.Arguments.ToArray());
}
}
if (methodCallOperand.Method == containsKeyMethod)
{
return Expression.Call(notContainsKeyMethod, methodCallOperand.Arguments.ToArray());
}
if (methodCallOperand.Method == notContainsKeyMethod)
{
return Expression.Call(containsKeyMethod, methodCallOperand.Arguments.ToArray());
}
}
}
return base.VisitUnary(node);
}
/// <summary>
/// Normalizes .Equals into == and Contains() into the appropriate stub.
/// </summary>
protected override Expression VisitMethodCall(MethodCallExpression node)
{
// Convert .Equals() into ==
if (node.Method.Name == "Equals" &&
node.Method.ReturnType == typeof(bool) &&
node.Method.GetParameters().Length == 1)
{
var obj = new ObjectNormalizer().Visit(node.Object) as MethodCallExpression;
var parameter = new ObjectNormalizer().Visit(node.Arguments[0]) as MethodCallExpression;
if ((IsAVObjectGet(obj) && (obj.Object is ParameterExpression)) ||
(IsAVObjectGet(parameter) && (parameter.Object is ParameterExpression)))
{
return Expression.Equal(node.Object, node.Arguments[0]);
}
}
// Convert the .Contains() into a ContainsStub
if (node.Method != stringContains &&
node.Method.Name == "Contains" &&
node.Method.ReturnType == typeof(bool) &&
node.Method.GetParameters().Length <= 2)
{
var collection = node.Method.GetParameters().Length == 1 ?
node.Object :
node.Arguments[0];
var parameterIndex = node.Method.GetParameters().Length - 1;
var parameter = new ObjectNormalizer().Visit(node.Arguments[parameterIndex])
as MethodCallExpression;
if (IsAVObjectGet(parameter) && (parameter.Object is ParameterExpression))
{
var genericContains = containsMethod.MakeGenericMethod(parameter.Type);
return Expression.Call(genericContains, collection, parameter);
}
var target = new ObjectNormalizer().Visit(collection) as MethodCallExpression;
var element = node.Arguments[parameterIndex];
if (IsAVObjectGet(target) && (target.Object is ParameterExpression))
{
var genericContains = containsMethod.MakeGenericMethod(element.Type);
return Expression.Call(genericContains, target, element);
}
}
// Convert obj["foo.bar"].ContainsKey("baz") into obj.ContainsKey("foo.bar.baz")
if (node.Method.Name == "ContainsKey" &&
node.Method.ReturnType == typeof(bool) &&
node.Method.GetParameters().Length == 1)
{
var getter = new ObjectNormalizer().Visit(node.Object) as MethodCallExpression;
Expression target = null;
string path = null;
if (IsAVObjectGet(getter) && getter.Object is ParameterExpression)
{
target = getter.Object;
path = GetValue(getter.Arguments[0]) + "." + GetValue(node.Arguments[0]);
return Expression.Call(containsKeyMethod, target, Expression.Constant(path));
}
else if (node.Object is ParameterExpression)
{
target = node.Object;
path = GetValue(node.Arguments[0]) as string;
}
if (target != null && path != null)
{
return Expression.Call(containsKeyMethod, target, Expression.Constant(path));
}
}
return base.VisitMethodCall(node);
}
}
/// <summary>
/// Converts a normalized method call expression into the appropriate AVQuery clause.
/// </summary>
private static AVQuery<T> WhereMethodCall<T>(
this AVQuery<T> source, Expression<Func<T, bool>> expression, MethodCallExpression node)
where T : AVObject
{
if (IsAVObjectGet(node) && (node.Type == typeof(bool) || node.Type == typeof(bool?)))
{
// This is a raw boolean field access like 'where obj.Get<bool>("foo")'
return source.WhereEqualTo(GetValue(node.Arguments[0]) as string, true);
}
MethodInfo translatedMethod;
if (functionMappings.TryGetValue(node.Method, out translatedMethod))
{
var objTransformed = new ObjectNormalizer().Visit(node.Object) as MethodCallExpression;
if (!(IsAVObjectGet(objTransformed) &&
objTransformed.Object == expression.Parameters[0]))
{
throw new InvalidOperationException(
"The left-hand side of a supported function call must be a AVObject field access.");
}
var fieldPath = GetValue(objTransformed.Arguments[0]);
var containedIn = GetValue(node.Arguments[0]);
var queryType = translatedMethod.DeclaringType.GetGenericTypeDefinition()
.MakeGenericType(typeof(T));
translatedMethod = ReflectionHelpers.GetMethod(queryType,
translatedMethod.Name,
translatedMethod.GetParameters().Select(p => p.ParameterType).ToArray());
return translatedMethod.Invoke(source, new[] { fieldPath, containedIn }) as AVQuery<T>;
}
if (node.Arguments[0] == expression.Parameters[0])
{
// obj.ContainsKey("foo") --> query.WhereExists("foo")
if (node.Method == containsKeyMethod)
{
return source.WhereExists(GetValue(node.Arguments[1]) as string);
}
// !obj.ContainsKey("foo") --> query.WhereDoesNotExist("foo")
if (node.Method == notContainsKeyMethod)
{
return source.WhereDoesNotExist(GetValue(node.Arguments[1]) as string);
}
}
if (node.Method.IsGenericMethod)
{
if (node.Method.GetGenericMethodDefinition() == containsMethod)
{
// obj.Get<IList<T>>("path").Contains(someValue)
if (IsAVObjectGet(node.Arguments[0] as MethodCallExpression))
{
return source.WhereEqualTo(
GetValue(((MethodCallExpression)node.Arguments[0]).Arguments[0]) as string,
GetValue(node.Arguments[1]));
}
// someList.Contains(obj.Get<T>("path"))
if (IsAVObjectGet(node.Arguments[1] as MethodCallExpression))
{
var collection = GetValue(node.Arguments[0]) as System.Collections.IEnumerable;
return source.WhereContainedIn(
GetValue(((MethodCallExpression)node.Arguments[1]).Arguments[0]) as string,
collection.Cast<object>());
}
}
if (node.Method.GetGenericMethodDefinition() == notContainsMethod)
{
// !obj.Get<IList<T>>("path").Contains(someValue)
if (IsAVObjectGet(node.Arguments[0] as MethodCallExpression))
{
return source.WhereNotEqualTo(
GetValue(((MethodCallExpression)node.Arguments[0]).Arguments[0]) as string,
GetValue(node.Arguments[1]));
}
// !someList.Contains(obj.Get<T>("path"))
if (IsAVObjectGet(node.Arguments[1] as MethodCallExpression))
{
var collection = GetValue(node.Arguments[0]) as System.Collections.IEnumerable;
return source.WhereNotContainedIn(
GetValue(((MethodCallExpression)node.Arguments[1]).Arguments[0]) as string,
collection.Cast<object>());
}
}
}
throw new InvalidOperationException(node.Method + " is not a supported method call in a where expression.");
}
/// <summary>
/// Converts a normalized binary expression into the appropriate AVQuery clause.
/// </summary>
private static AVQuery<T> WhereBinaryExpression<T>(
this AVQuery<T> source, Expression<Func<T, bool>> expression, BinaryExpression node)
where T : AVObject
{
var leftTransformed = new ObjectNormalizer().Visit(node.Left) as MethodCallExpression;
if (!(IsAVObjectGet(leftTransformed) &&
leftTransformed.Object == expression.Parameters[0]))
{
throw new InvalidOperationException(
"Where expressions must have one side be a field operation on a AVObject.");
}
var fieldPath = GetValue(leftTransformed.Arguments[0]) as string;
var filterValue = GetValue(node.Right);
if (filterValue != null && !AVEncoder.IsValidType(filterValue))
{
throw new InvalidOperationException(
"Where clauses must use types compatible with AVObjects.");
}
switch (node.NodeType)
{
case ExpressionType.GreaterThan:
return source.WhereGreaterThan(fieldPath, filterValue);
case ExpressionType.GreaterThanOrEqual:
return source.WhereGreaterThanOrEqualTo(fieldPath, filterValue);
case ExpressionType.LessThan:
return source.WhereLessThan(fieldPath, filterValue);
case ExpressionType.LessThanOrEqual:
return source.WhereLessThanOrEqualTo(fieldPath, filterValue);
case ExpressionType.Equal:
return source.WhereEqualTo(fieldPath, filterValue);
case ExpressionType.NotEqual:
return source.WhereNotEqualTo(fieldPath, filterValue);
default:
throw new InvalidOperationException(
"Where expressions do not support this operator.");
}
}
/// <summary>
/// Filters a query based upon the predicate provided.
/// </summary>
/// <typeparam name="TSource">The type of AVObject being queried for.</typeparam>
/// <param name="source">The base <see cref="AVQuery{TSource}"/> to which
/// the predicate will be added.</param>
/// <param name="predicate">A function to test each AVObject for a condition.
/// The predicate must be able to be represented by one of the standard Where
/// functions on AVQuery</param>
/// <returns>A new AVQuery whose results will match the given predicate as
/// well as the Source's filters.</returns>
public static AVQuery<TSource> Where<TSource>(
this AVQuery<TSource> source, Expression<Func<TSource, bool>> predicate)
where TSource : AVObject
{
// Handle top-level logic operators && and ||
var binaryExpression = predicate.Body as BinaryExpression;
if (binaryExpression != null)
{
if (binaryExpression.NodeType == ExpressionType.AndAlso)
{
return source
.Where(Expression.Lambda<Func<TSource, bool>>(
binaryExpression.Left, predicate.Parameters))
.Where(Expression.Lambda<Func<TSource, bool>>(
binaryExpression.Right, predicate.Parameters));
}
if (binaryExpression.NodeType == ExpressionType.OrElse)
{
var left = source.Where(Expression.Lambda<Func<TSource, bool>>(
binaryExpression.Left, predicate.Parameters));
var right = source.Where(Expression.Lambda<Func<TSource, bool>>(
binaryExpression.Right, predicate.Parameters));
return left.Or(right);
}
}
var normalized = new WhereNormalizer().Visit(predicate.Body);
var methodCallExpr = normalized as MethodCallExpression;
if (methodCallExpr != null)
{
return source.WhereMethodCall(predicate, methodCallExpr);
}
var binaryExpr = normalized as BinaryExpression;
if (binaryExpr != null)
{
return source.WhereBinaryExpression(predicate, binaryExpr);
}
var unaryExpr = normalized as UnaryExpression;
if (unaryExpr != null && unaryExpr.NodeType == ExpressionType.Not)
{
var node = unaryExpr.Operand as MethodCallExpression;
if (IsAVObjectGet(node) && (node.Type == typeof(bool) || node.Type == typeof(bool?)))
{
// This is a raw boolean field access like 'where !obj.Get<bool>("foo")'
return source.WhereNotEqualTo(GetValue(node.Arguments[0]) as string, true);
}
}
throw new InvalidOperationException(
"Encountered an unsupported expression for AVQueries.");
}
/// <summary>
/// Normalizes an OrderBy's keySelector expression and then extracts the path
/// from the AVObject.Get() call.
/// </summary>
private static string GetOrderByPath<TSource, TSelector>(
Expression<Func<TSource, TSelector>> keySelector)
{
string result = null;
var normalized = new ObjectNormalizer().Visit(keySelector.Body);
var callExpr = normalized as MethodCallExpression;
if (IsAVObjectGet(callExpr) && callExpr.Object == keySelector.Parameters[0])
{
// We're operating on the parameter
result = GetValue(callExpr.Arguments[0]) as string;
}
if (result == null)
{
throw new InvalidOperationException(
"OrderBy expression must be a field access on a AVObject.");
}
return result;
}
/// <summary>
/// Orders a query based upon the key selector provided.
/// </summary>
/// <typeparam name="TSource">The type of AVObject being queried for.</typeparam>
/// <typeparam name="TSelector">The type of key returned by keySelector.</typeparam>
/// <param name="source">The query to order.</param>
/// <param name="keySelector">A function to extract a key from the AVObject.</param>
/// <returns>A new AVQuery based on Source whose results will be ordered by
/// the key specified in the keySelector.</returns>
public static AVQuery<TSource> OrderBy<TSource, TSelector>(
this AVQuery<TSource> source, Expression<Func<TSource, TSelector>> keySelector)
where TSource : AVObject
{
return source.OrderBy(GetOrderByPath(keySelector));
}
/// <summary>
/// Orders a query based upon the key selector provided.
/// </summary>
/// <typeparam name="TSource">The type of AVObject being queried for.</typeparam>
/// <typeparam name="TSelector">The type of key returned by keySelector.</typeparam>
/// <param name="source">The query to order.</param>
/// <param name="keySelector">A function to extract a key from the AVObject.</param>
/// <returns>A new AVQuery based on Source whose results will be ordered by
/// the key specified in the keySelector.</returns>
public static AVQuery<TSource> OrderByDescending<TSource, TSelector>(
this AVQuery<TSource> source, Expression<Func<TSource, TSelector>> keySelector)
where TSource : AVObject
{
return source.OrderByDescending(GetOrderByPath(keySelector));
}
/// <summary>
/// Performs a subsequent ordering of a query based upon the key selector provided.
/// </summary>
/// <typeparam name="TSource">The type of AVObject being queried for.</typeparam>
/// <typeparam name="TSelector">The type of key returned by keySelector.</typeparam>
/// <param name="source">The query to order.</param>
/// <param name="keySelector">A function to extract a key from the AVObject.</param>
/// <returns>A new AVQuery based on Source whose results will be ordered by
/// the key specified in the keySelector.</returns>
public static AVQuery<TSource> ThenBy<TSource, TSelector>(
this AVQuery<TSource> source, Expression<Func<TSource, TSelector>> keySelector)
where TSource : AVObject
{
return source.ThenBy(GetOrderByPath(keySelector));
}
/// <summary>
/// Performs a subsequent ordering of a query based upon the key selector provided.
/// </summary>
/// <typeparam name="TSource">The type of AVObject being queried for.</typeparam>
/// <typeparam name="TSelector">The type of key returned by keySelector.</typeparam>
/// <param name="source">The query to order.</param>
/// <param name="keySelector">A function to extract a key from the AVObject.</param>
/// <returns>A new AVQuery based on Source whose results will be ordered by
/// the key specified in the keySelector.</returns>
public static AVQuery<TSource> ThenByDescending<TSource, TSelector>(
this AVQuery<TSource> source, Expression<Func<TSource, TSelector>> keySelector)
where TSource : AVObject
{
return source.ThenByDescending(GetOrderByPath(keySelector));
}
/// <summary>
/// Correlates the elements of two queries based on matching keys.
/// </summary>
/// <typeparam name="TOuter">The type of AVObjects of the first query.</typeparam>
/// <typeparam name="TInner">The type of AVObjects of the second query.</typeparam>
/// <typeparam name="TKey">The type of the keys returned by the key selector
/// functions.</typeparam>
/// <typeparam name="TResult">The type of the result. This must match either
/// TOuter or TInner</typeparam>
/// <param name="outer">The first query to join.</param>
/// <param name="inner">The query to join to the first query.</param>
/// <param name="outerKeySelector">A function to extract a join key from the results of
/// the first query.</param>
/// <param name="innerKeySelector">A function to extract a join key from the results of
/// the second query.</param>
/// <param name="resultSelector">A function to select either the outer or inner query
/// result to determine which query is the base query.</param>
/// <returns>A new AVQuery with a WhereMatchesQuery or WhereMatchesKeyInQuery
/// clause based upon the query indicated in the <paramref name="resultSelector"/>.</returns>
public static AVQuery<TResult> Join<TOuter, TInner, TKey, TResult>(
this AVQuery<TOuter> outer,
AVQuery<TInner> inner,
Expression<Func<TOuter, TKey>> outerKeySelector,
Expression<Func<TInner, TKey>> innerKeySelector,
Expression<Func<TOuter, TInner, TResult>> resultSelector)
where TOuter : AVObject
where TInner : AVObject
where TResult : AVObject
{
// resultSelector must select either the inner object or the outer object. If it's the inner
// object, reverse the query.
if (resultSelector.Body == resultSelector.Parameters[1])
{
// The inner object was selected.
return inner.Join<TInner, TOuter, TKey, TInner>(
outer,
innerKeySelector,
outerKeySelector,
(i, o) => i) as AVQuery<TResult>;
}
if (resultSelector.Body != resultSelector.Parameters[0])
{
throw new InvalidOperationException("Joins must select either the outer or inner object.");
}
// Normalize both selectors
Expression outerNormalized = new ObjectNormalizer().Visit(outerKeySelector.Body);
Expression innerNormalized = new ObjectNormalizer().Visit(innerKeySelector.Body);
MethodCallExpression outerAsGet = outerNormalized as MethodCallExpression;
MethodCallExpression innerAsGet = innerNormalized as MethodCallExpression;
if (IsAVObjectGet(outerAsGet) && outerAsGet.Object == outerKeySelector.Parameters[0])
{
var outerKey = GetValue(outerAsGet.Arguments[0]) as string;
if (IsAVObjectGet(innerAsGet) && innerAsGet.Object == innerKeySelector.Parameters[0])
{
// Both are key accesses, so treat this as a WhereMatchesKeyInQuery
var innerKey = GetValue(innerAsGet.Arguments[0]) as string;
return outer.WhereMatchesKeyInQuery(outerKey, innerKey, inner) as AVQuery<TResult>;
}
if (innerKeySelector.Body == innerKeySelector.Parameters[0])
{
// The inner selector is on the result of the query itself, so treat this as a
// WhereMatchesQuery
return outer.WhereMatchesQuery(outerKey, inner) as AVQuery<TResult>;
}
throw new InvalidOperationException(
"The key for the joined object must be a AVObject or a field access " +
"on the AVObject.");
}
// TODO (hallucinogen): If we ever support "and" queries fully and/or support a "where this object
// matches some key in some other query" (as opposed to requiring a key on this query), we
// can add support for even more types of joins.
throw new InvalidOperationException(
"The key for the selected object must be a field access on the AVObject.");
}
}
}