$indexOfArray (aggregation)

Definition定义

$indexOfArray

Searches an array for an occurrence of a specified value and returns the array index (zero-based) of the first occurrence. 在数组中搜索指定值的匹配项，并返回第一个匹配项的数组索引（从零开始）。If the value is not found, returns -1.如果找不到该值，则返回-1。

$indexOfArray has the following operator expression syntax:具有以下运算符表达式语法：

{ $indexOfArray: [ <array expression>, <search expression>, <start>, <end> ] }

Field字段	Type类型	Description描述
<array>	string	Can be any valid expression as long as it resolves to an array. 可以是任何有效表达式，只要它解析为数组。For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。 If the array expression resolves to a value of null or refers to a field that is missing, $indexOfArray returns null.如果数组表达式解析为null值或引用缺少的字段，$indexOfArray将返回null。 If the array expression does not resolve to an array or null nor refers to a missing field, $indexOfArray returns an error.如果数组表达式未解析为数组或null，也未引用缺少的字段，$indexOfArray将返回错误。
<search value>	string	Can be any valid expression. 可以是任何有效表达式。For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。
<start>	integer	Optional. 可选。An integer, or a number that can be represented as integers (such as 2.0), that specifies the starting index position for the search. 一个整数或可以表示为整数的数字（例如2.0），用于指定搜索的起始索引位置。Can be any valid expression that resolves to a non-negative integral number.可以是解析为非负整数的任何有效表达式。 If unspecified, the starting index position for the search is the beginning of the string.如果未指定，则搜索的起始索引位置是字符串的开头。
<end>	integer	Optional. 可选。An integer, or a number that can be represented as integers (such as 2.0), that specifies the ending index position for the search. 一个整数或可以表示为整数的数字（例如2.0），用于指定搜索的结束索引位置。Can be any valid expression that resolves to a non-negative integral number. 可以是解析为非负整数的任何有效表达式。If you specify a <end> index value, you should also specify a <start> index value; otherwise, $indexOfArray uses the <end> value as the <start> index value instead of the <end> value.如果指定<end>索引值，还应指定<start>索引值；否则，$indexOfArray将<end>值用作<start>索引值，而不是<end>。 If unspecified, the ending index position for the search is the end of the string.如果未指定，则搜索的结束索引位置是字符串的结尾。

Behavior行为

If the <search expression> is found multiple times within the <array expression>, then $indexOfArray returns the index of the first <search expression> from the starting index position.如果在<array expression>中多次找到<search expression>，则$indexOfArray将从起始索引位置返回第一个<search expression>的索引。

$indexOfArray returns null:返回null:

• If <array expression> is null, or如果<array expression>为null，或
• If <array expression> refers to a non-existing field in the input document.如果<array expression>引用输入文档中不存在的字段。

$indexOfArray returns an error:返回错误：

• If <array expression> is not an array and not null, or如果<array expression>不是数组且不为空，或者
• If <start> or <end> is a negative integer (or a value that can be represented as a negative integer, like -5.0).如果<start>或<end>是负整数（或可以表示为负整数的值，如-5.0）。

$indexOfArray returns -1:返回-1：

• If the <search expression> is not found in the array, or如果在数组中找不到<search expression>，或
• If <start> is a number greater than <end>, or如果<start>是大于<end>的数字，或
• If <start> is a number greater than the length of the array.如果<start>是一个大于数组长度的数字。

Examples示例

Consider an inventory collection with the following documents:考虑具有以下文档的inventory集合：

{ "_id" : 1, "items" : ["one", "two", "three"] }
{ "_id" : 2, "items" : [1, 2, 3] }
{ "_id" : 3, "items" : [null, null, 2] }
{ "_id" : 4, "items" : null }
{ "_id" : 5, "amount" : 3 }

The following operation uses the $indexOfArray operator to return the array index at which the string foo is located in each items array:以下操作使用$indexOfArray运算符返回字符串foo位于每个items数组中的数组索引：

db.inventory.aggregate(
   [
     {
       $project:
          {
            index: { $indexOfArray: [ "$items", 2 ] },
          }
      }
   ]
)

The operation returns the following results:该操作返回以下结果：

{ "_id" : 1, "index" : "-1" }
{ "_id" : 2, "index" : "1" }
{ "_id" : 3, "index" : "2" }
{ "_id" : 4, "index" : null }
{ "_id" : 5, "index" : null }