# Dynamic mapping: Confusing type inference behaviour
**URL:** https://discuss.elastic.co/t/dynamic-mapping-confusing-type-inference-behaviour/197371
**Category:** Elasticsearch
**Created:** [August 29, 2019, 2:53pm UTC](https://discuss.elastic.co/t/dynamic-mapping-confusing-type-inference-behaviour/197371 "2019-08-29T14:53:58Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@timost](https://discuss.elastic.co/u/timost)
#### Post date: [August 29, 2019, 2:53pm UTC](https://discuss.elastic.co/t/dynamic-mapping-confusing-type-inference-behaviour/197371/1 "2019-08-29T14:53:58Z")
Hi,
I'm using Elasticsearch 6.8.2.
I've been playing with mappings and I've stumbled across this behavior for which I can't find an explanation:
```auto
# Step 0: Creating an index with dynamic mappings enabled
PUT /test-datatypes
{
"settings" : {
"number_of_shards" : 1
},
"mappings" : {
"_doc": {
"properties" : {
"shortfield" : { "type" : "short" }
}
}
}
}
# Step 1: Add a valid short int
POST /test-datatypes/_doc/1
{
"shortfield": 1
}
# Step 2: Add a float with many decimals
POST /test-datatypes/_doc/2
{
"shortfield": 1.1234532145432145765432145867543211234256
}
# Step 3: Add the same float as a JSON string
POST /test-datatypes/_doc/3
{
"shortfield": "1.1234532145432145765432145867543211234256"
}
# Step 4: Try to add a float with a big integer part
POST /test-datatypes/_doc/4
{
"shortfield": 112312.1234532145432145765432145867543211234256
}
# => As expected throws
{
"error": {
"root_cause": [
{
"type": "mapper_parsing_exception",
"reason": "failed to parse field [shortfield] of type [short] in document with id '4'"
}
],
"type": "mapper_parsing_exception",
"reason": "failed to parse field [shortfield] of type [short] in document with id '4'",
"caused_by": {
"type": "json_parse_exception",
"reason": "Numeric value (112312.1234532145432145765432145867543211234256) out of range of Java short\n at [Source: org.elasticsearch.common.bytes.BytesReference$MarkSupportingStreamInputWrapper@2a672a72; line: 2, column: 64]"
}
},
"status": 400
}
```
If I search the index I get this:
```auto
GET test-datatypes/_search
{
"took" : 0,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : 3,
"max_score" : 1.0,
"hits" : [
{
"_index" : "test-datatypes",
"_type" : "_doc",
"_id" : "1",
"_score" : 1.0,
"_source" : {
# As expected
"shortfield" : 1
}
},
{
"_index" : "test-datatypes",
"_type" : "_doc",
"_id" : "2",
"_score" : 1.0,
"_source" : {
# Expexted: I would have expected this to throw an error at index time
# My guess: decimals are truncated to fit in the number of bits of a short
"shortfield" : 1.1234532145432146
}
},
{
"_index" : "test-datatypes",
"_type" : "_doc",
"_id" : "3",
"_score" : 1.0,
"_source" : {
# Expected: I would have expected this to throw an error at index time
# Suprising: Not truncated, "raw field"
"shortfield" : "1.1234532145432145765432145867543211234256"
}
}
]
}
}
```
If I look at the mappings I get:
```auto
GET test-datatypes/_search
{
"test-datatypes" : {
"mappings" : {
"_doc" : {
"properties" : {
"shortfield" : {
"type" : "long"
}
}
}
}
}
}
```
The things I don't understand are:
1. Why are docs `2` and `3` allowed to be indexed while their types do not match the `short` numerical type.
2. Why doc `2`'s `shortfield` is returned truncated and not doc `3`'s.
I've been trying to find answers in the documentation without success.
Could someone please enlighten me as to why Elasticsearch behaves this way ?
Thank you
---
### Author:  [@spinscale](https://discuss.elastic.co/u/spinscale)
#### Post date: [August 30, 2019, 8:58am UTC](https://discuss.elastic.co/t/dynamic-mapping-confusing-type-inference-behaviour/197371/2 "2019-08-30T08:58:24Z")
Take a look at the [coercing feature](https://www.elastic.co/guide/en/elasticsearch/reference/7.3/coerce.html), which truncates fields to integers. See also [https://www.elastic.co/guide/en/elasticsearch/reference/7.3/number.html](https://www.elastic.co/guide/en/elasticsearch/reference/7.3/number.html) for the default setting of `coerce`
As you can see in the mapping, by default a long is picked, and the floating point numbers get coerced into a long.
hope this helps.
---
### Author:  [@timost](https://discuss.elastic.co/u/timost)
#### Post date: [September 13, 2019, 11:17am UTC](https://discuss.elastic.co/t/dynamic-mapping-confusing-type-inference-behaviour/197371/3 "2019-09-13T11:17:32Z")
Thank you for your answer. I missed the coerce setting !
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [October 11, 2019, 11:17am UTC](https://discuss.elastic.co/t/dynamic-mapping-confusing-type-inference-behaviour/197371/4 "2019-10-11T11:17:40Z")
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